the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

three dimensional deformation measured in an alaskan glacier measurements of movement along 28 boreholes reveal the three dimensional flow field in a 6 million cubic meter reach of worthington glacier a temperate valley glacier located in alaska sliding at the bed accounted for 60 to 70 percent of the glacier s surface motion strain rates in the ice were low from the surface to a depth of about 120 meters but then increased rapidly toward the bed ice deformation was not affected by temporal changes in the sliding rate the three dimensional pattern of motion indicates that plane strain which is often assumed by models is a poor approximation of this viscous flow

a 200 000 year δ18o record of closed basin lacustrine calcite death valley california abstract a modified method from mccrea mccrea j m 1950 the isotopic chemistry of carbonates and a paleotemperature scale j chem phys 18 849 857 has been developed for analyzing carbon and oxygen isotopic compositions of lacustrine calcite in bulk saline lake sediments a two level climatic fluctuation model is suggested based on a continuous 200 000 year 18 o record of lacustrine calcite from a 186 m sediment core from badwater basin death valley california this record provides new approaches to the debate on the timing and driving forces of late quaternary climatic changes excursions in calcite 18 o track those of 18 o in sulfate in the death valley core as well as to those in marine carbonate specmap and polar ice in the summit ice core grip greenland the death valley record shows periodicities of 96 000 39 000 21 000 14 000 and 8000 years the longer term 96 000 39 000 and 21 000 years fluctuations match milankovitch orbital forcing and are thus likely to be global in origin the shorter term 14 000 and 8000 years fluctuations probably reflect regional climatic and or hydrologic forcing

styles of subglacial glaciotectonic deformation within the context of the anglian ice sheet a substantial proportion of the glacial sediments of east anglia england are chaotic and highly deformed this has been attributed to a direct glaciotectonic deformation or b slumping of glaciomarine sediments we show that interpretation a leads to a classification of subglacial glaciotectonic deposits into sites of constructional deformation where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence and excavational deformation where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other by using glaciological and geotechnical theory we show that the expression of these deformational styles in east anglia is a natural response to the stress fields imposed by the ice sheet and that in consequence their spatial relationships are explicable the depth of deformation is related to the geotechnical properties of till and substrate the stress and effective stress fields and found to be consistent with observations

isotopic evidence of holocene climatic change in the san juan mountains colorado abstract the d of cellulose from 14c dated wood collected in the san juan mountains of southwestern colorado decreased by about 45 from 9600 to 3100 yr b p and an additional 25 to the present the wood samples are from trees that grew above present day tree line and reflect a time of warmer average summer temperatures these changes in d are interpreted to indicate a major change during the holocene in the sources of moisture in the seasonality of precipitation or in both

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

sea level during the penultimate interglacial period based on a submerged stalagmite from argentarola cave italy accurate constraints are presented for the absolute age duration and sea level for the highstand corresponding to marine isotope stage mis 7 1 our work is based on a stalagmite collected in a currently submerged cave from italy argentarola cave flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms precise uranium thorium u th ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during mis 7 2 and mis 6 the penultimate glacial period in addition the period of marine transgression is bracketed between 202 and 190 kyr bp defining a mis 7 1 duration of 11 2 kyr comparison with previous studies provides a new constraint on the sea level during mis 7 1 that has approximately remained between 318 and 39 m relative to present sea level the timing of the mis 7 1 highstand is in full agreement with the specmap chronology which contrasts with the growing body of evidence showing a significant phase difference for mis 5 5 a tempting conclusion is that second order sea level highstands such as mis 7 1 may be purely driven by astronomical changes in contrast with major terminations such as termination ii atmospheric co2 levels may partly explain this contrast since the two sea level transitions mis 7 2 7 1 and mis 6 5 5 are characterized by very different co2 rises 20 vs 100 ppm fl 2002 elsevier science b v all rights reserved

dynamics of core formation and equilibration by negative diapirism 1 we investigate dynamically the timing and metal silicate equilibration processes during core formation by negative diapirism using numerical modeling in 3 d axisymmetric geometry we follow the sinking of iron rich diapirs through a viscous silicate mantle we carried out a parameter study in which shear heating as well as several viscous rheologies are considered and systematically varied general scaling laws are derived for the diapir sinking velocity as well as for the silicate melt generation and distribution around the diapir using these scaling laws we show that metal diapirs of a radius 1 100 m sinking through a partially molten silicate mantle can chemically equilibrate within the timescales suggested by geochemical constraints therefore negative diapirism can contribute significantly to metal silicate equilibration processes during core formation

interior structure and seasonal mass redistribution of mars from radio tracking of mars pathfinder doppler and range measurements to the mars pathfinder lander made using its radio communications system have been combined with similar measurements from the viking landers to estimate improved values of the precession of mars pole of rotation and the variation in mars rotation rate the observed precession of 7576 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition the estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

till fabric associated with deformable beds this paper investigates the development of till fabric associated with glaciers overlying deformable beds first the till fabrics from both modern and ancient soft bed and hard bed subglacial environments are investigated and then soft bedded sites with specific strain histories are examined the results indicate that lodgement tills had a strong fabric whilst there is a wide range of much weaker fabric strengths associated with soft bed tills it is suggested from a theoretical study of soft bed till deposition that longitudinal and vertical processes in the subglacial deforming layer are important in fabric development field sites were chosen to isolate these two factors and fabrics investigated in areas of known relative shear strain and known relative thickness of the deforming layer the results indicate that 1 for a fixed deforming layer fabric strength does increase with increasing deformation except at very high strains where the development of a transverse fabric can lead to a reduction in the overall fabric strain and 2 lodgement tills and soft bed tills associated with a thin deforming layer have a high fabric strength whilst soft bed tills associated with a thick deforming layer have a low fabric strength where the deforming layer is thin clasts are oriented parallel with the glacier direction either by lodging against a hard bed or ploughing against a soft bed however where the deforming layer is thicker and shear strains are high melt out processes encourage a parallel fabric but the increased shear strain and changes in the deforming layer thickness cause the clasts to develop both a parallel and transverse fabric these processes combine to reduce the overall fabric strength till fabric studies are a further sedimentological technique to separate the depositional processes associated with a homogeneous till

influence of the glacier bed lithology on the formation of a subglacial till sequence ring shear experiments as a tool for the classification of subglacial tills abstract a glaciogenic sediment sequence deposited by a local glacier in the rhine catchment area near sargans eastern swiss alps was investigated in order to examine the shear behaviour of two different tills in addition to ring shear experiments examination of clast lithology clay mineralogy and physical properties of all samples were determined sem analyses of artificially produced deformation patterns in the till samples show only a very thin shear zones of 2 3 m thickness despite long shear distances of up to 145 mm a clear relationship between local bedrock and the formation of a thin basal layer of heavily deformed till can be demonstrated this locally derived till layer exhibits distinctly different shearing properties compared to the massive overlying till unit that is composed of more distantly transported lithic material from the upper catchment area of the glacier the difference in the angle of internal friction between the two tills is 10 at residual shear strength although the clay mineralogy of both tills is similar it can further be demonstrated that after the deposition of a 10 15 cm thin till layer directly on bedrock the flow dynamics of the glacier tongue may have changed due to differences in glacier bed debris lithology differences in the shear behaviour of the sediments allied to microscopic analyses point to an important environmental change from a deformation till to an overlying non deformed till

milankovitch paced termination ii in a nevada speleothem 1 the devils hole dh calcite record from the great basin nevada provided the first radiometrically dated time series of late pleistocene climate fluctuations in doing so dh suggested that the penultimate deglaciation termination ii t ii occurred at 142 3 ka which is 10 kyr before the associated rise in summer insolation helping to launch the causality problem for milankovitch the interpretation of the dh record has been subject to considerable discussion ever since we present the first attempt to reproduce the dh record of an early t ii in the great basin based on a stalagmite from lehman caves nevada which is 400 km northeast of devils hole our speleothem records at least the latter part of t ii over its period of growth from 133 129 ka which appears to disagree with the early timing of t ii in dh dh also exhibits important differences from many other paleoclimate records over the past two deglaciations though these are reduced somewhat after ice volume correcting dh 18o we suggest that the climatic signal in the dh record remains to be fully explained

consequences of giant impacts in early mars core merging and martian dynamo evolution a giant impact is an increasingly popular explanation for the formation of the northern lowland on mars it is plausible that at the impact time both mars and the impactor were differentiated with solid silicate mantles and liquid iron cores such a large impact likely resulted in merging of the cores of both bodies a process which will have implications on the thermal state of the planet we model the evolution of the martian mantle following a giant impact and characterize the thermochemical consequences of the sinking of an impactor s core as a single diapir the impact heating and the viscous heating induced during the core merging may affect the early thermal state of mars during several tens of million years our results show that large viscosity contrasts between the impactor s core and the surrounding mantle silicates can reduce the duration of the merging down to 1 kyr but do not modify the merging temperature when the viscosity contrast between the diapir and the surrounding silicates is larger than a factor of 1000 the descent of the diapir can lead to some entrainment of the relatively shallow silicates to deepest regions close to the core mantle boundary finally the direct impact heating of martian core leads to thermal stratification of the core and kills the core dynamo it takes on the order of 150 200 myr to reinitiate a strong dynamo anew the merging of the impactor s core with the martian core only delays the reinitiation of the dynamo for a very short time

core formation in earth s moon mars and vesta stimulated by new experimental results on metal silicate partitioning of elements at elevated temperatures and pressures we have revisited the question of core formation in earth s moon mars and vesta the probable source of the eucritic meteorites earlier studies suggested metal silicate equilibrium in mars but led to the paradox that mars accreted homogeneously while the earth accreted heterogeneously using new elevated pressure and temperature metal silicate partition coefficients we show that abundances of the moderately siderophile elements in the mantles of the moon mars and vesta are consistent with early magma oceans on these bodies the most successful model for explaining the lunar mantle siderophile element abundances requires a core of 5 of the mass of the moon 500 km radius siderophile element abundances in mars are consistent with intermediate pressure metal silicate equilibrium as has also been recently suggested for the earth the most successful model for explaining the martian siderophile element abundances requires a bulk planetary composition that has greater than ci chondritic abundances of the moderately siderophile elements and a core of 30 of the mass of mars siderophile element abundances in the mantle of vesta are consistent with low pressure liquid metal liquid silicate equilibrium as expected for an asteroid sized body and a core of 10 of the mass of vesta comparison of our best fit oxygen fugacities for vesta with thermodynamic calculations of oxygen fugacity for silicate bearing iron meteorites indicates that parts of the inner solar system were homogeneous with respect to redox state at 4 5 ga approximately 2 log fo2units below the fe feo buffer much higher than estimates for the solar nebula similar comparisons for mars and the earth indicate that these bodies have undergone oxidation since 4 5 ga because the oxygen fugacities associated with metal silicate equilibrium in both mars and the earth moon system are much lower than those recorded in martian and terrestrial basaltic and periodotitic samples the oxidation on mars is most likely due to atmospheric effects whereas earth s much wider range of oxygen fugacities must be due to both atmospheric and plate tectonic effects

earth s core formation aided by flow channelling instabilities induced by iron diapirs abstract the core formation mechanism remains poorly known an unstable gravitational configuration of a dense molten metallic layer overlying a cold chondritic protocore is predicted by most studies which leads to the formation of a rayleigh taylor rt instability recent results dahl t w 2005 turbulent mixing during planet accretion and core formation interpretation of the hf w chronometer and implications for the age of the moon m sc thesis university of copenhagen indicate that additionally iron cores of predifferentiated planetesimals are also able to plunge mostly intact into the cold protocore and create large iron diapirs for both scenarios we propose the application of the stress induced melt channelling mechanism stevenson d j 1989 spontaneous small scale melt segregation in partial melts undergoing deformation geophys res lett 16 1 067 1 070 in the region surrounding an incipient iron diapir we therefore perform numerical experiments solving the two phase two composition flow equations within a 2d rectangular box with symmetrical boundary conditions we apply the compaction boussinesq approximation cba and include a depth dependent gravity for simplicity we use a constant viscosity for the solid phase and a melt fraction dependent rheology for the partially molten region around the diapir we investigate the physical conditions under which the melt channels can form and whether they are applicable to the early earth as a result for sufficiently small melt retention numbers iron rich melt channels develop within a region of approximately twice the diapir s size this could lead to effective draining of the surrounding region and might initiate cascading daughter diapirs the region of the protocore drained by this cascading mechanism is expected to significantly increase with depth and thus indicates an effective mechanism to also extract iron melt from deeper parts of the initially chondritic protocore this mechanism could effectively accelerate the process of core formation

high porosity of basal till at burroughs glacier southeastern alaska debris rich basal ice at burroughs glacier southeastern alaska has 60 vol to 70 vol debris recently deposited basal till exceeds 60 vol sediment with 30 to almost 40 porosity where basal ice is very rich in debris basal till is deposited through melt out with only slight compaction of the debris porosity this high in till is commonly associated with subglacially deforming and dilated sediment however the recently deposited basal melt out till at burroughs glacier has not been deformed after deposition but has porosity values similar to tills elsewhere interpreted to be subglacially deforming and dilated in an unfrozen state high porosity can occur in basal melt out till deposited directly by basal melt out

co2 condensation is a serious limit to the deglaciation of earth like planets abstract it is widely believed that the carbonate silicate cycle is the main agent through volcanism to trigger deglaciations by co2 greenhouse warming on earth and on earth like planets when they get in a frozen state here we use a 3d global climate model to simulate the ability of planets initially completely frozen to escape from glaciation episodes by accumulating enough gaseous co2 the model includes co2 condensation and sublimation processes and the water cycle we find that planets with earth like characteristics size mass obliquity rotation rate etc orbiting a sun like star may never be able to escape from a glaciation era if their orbital distance is greater than 1 27 astronomical units flux 847 w m 2 or 62 of the solar constant because co2 would condense at the poles here the cold traps forming permanent co2 ice caps this limits the amount of co2 in the atmosphere and thus its greenhouse effect furthermore our results indicate that for 1 high rotation rates p rot 24 h 2 low obliquity obliquity 0 6 this critical limit could occur at a significantly lower equivalent distance or higher insolation for each possible configuration we show that the amount of co2 that can be trapped in the polar caps depends on the efficiency of co2 ice to flow laterally as well as its gravitational stability relative to subsurface water ice we find that a frozen earth like planet located at 1 30 au of a sun like star could store as much as 1 5 4 5 and 15 bars of dry ice at the poles for internal heat fluxes of 100 30 and 10 mw m 2 respectively but these amounts are in fact lower limits for planets with a significant water ice cover we show that co2 ice deposits should be gravitationally unstable they get buried beneath the water ice cover in geologically short timescales of 104 yrs mainly controlled by the viscosity of water ice co2 would be permanently sequestered underneath the water ice cover in the form of co2 liquids co2 clathrate hydrates and or dissolved in subglacial water reservoirs if any this would considerably increase the amount of co2 trapped and further reduce the probability of deglaciation

heat partitioning in metal silicate plumes during earth differentiation abstract we present an analytical model for core formation that includes both metal diapirs and liquid conduits and produces a superheated core we start from the standard model of earth formation consisting of accretion by planetesimal or planetary embryo impacts large enough to create global or local magma oceans our model consists of two main fluid dynamical structures 1 large liquid metal diapirs and 2 narrow conduits with liquid silicate and small liquid metal droplets we assume that transport of metal from a near surface magma ocean to the growing core occurs within these structures the release of gravitational potential energy from the descent of the metal is converted to heat through viscous dissipation which is broadly distributed around the large liquid metal diapirs but localized in the conduit around the smaller metal droplets this model gives an average core temperature during accretion and a post accretion average core temperature for a broad range of impact histories and chemical quilibration assumptions we consider three types of earth accretion histories with impacts that are evenly spaced over 30 ma these include 1 equal sized impacts 2 equal sized impacts with a final mars sized impact and 3 exponentially decreasing impact sizes with a final mars sized impact our preferred model is based on core mantle chemical equilibrium estimates that correspond to a fractionation f the ratio of metal in the diapir to the total metal content in each impact of f 0 64 and accretion history type 3 this model produces a post accretion average core temperature that ranges from 5930 k to 5700 k for 8 to 90 impacts respectively the efficiency of the metal silicate conduits defined as the ratio of the heating of the core by the conduits to their potential energy released has an approximate value of 0 59 for our preferred model the residual post accretion structures include a basal magma ocean and a network of mantle conduits that may dictate the style of hadean tectonics

early differentiation of the moon evidence from trace elements in plagioclase bulk samples and plagioclase mineral grains from lunar cataclastic ferroan anorthosites were analyzed for trace elements by instrumental neutron activation analysis some pure plagioclase crystals have lower concentrations of cr co sc and heavy rees than previous analyses indicated concentrations of sr eu na ga and the rees in plagioclases from different anorthosites vary in a systematic way and the trace element patterns of plagioclases from pristine norites and troctolites are very different from the plagioclase pattern of anorthosites the following model is suggested to account for these observations 1 melting of a large fraction of the moon formation of a magma ocean precipitation of olivine and later pyroxene followed by flotation of cumulus plagioclase 2 mixing of kreep with a mafic component enriched in mg cr and co 3 precipitation of noritic and troctolitic cumulates and metallic iron from this magma and 4 eruption of these kreep and mg rich lavas and or distribution of these materials over the front side of the moon by basin forming impacts 3 9 4 0 b y ago

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

two dimensional stokes flow around a heated cylinder a possible application for diapirs in the mantle 1 it is widely assumed that the separation of metal and silicates in a homogeneously accreted protoplanet occurred rather rapidly the process of core formation through the descent of large hot iron rich bodies through a cold silicate protoplanet is discussed if iron diapirs sink toward the planet center with the stokes velocity they would require more than 800 ma to form a core in the case of a planet similar to the earth we therefore implement a temperature dependent rheology for the silicate material surrounding the diapir which leads to a reduction of the drag force exerted on the iron drop we compare the drag force for different sinking velocities to the body force on the diapir and find that the terminal velocity in the temperature dependent viscosity model is a factor of 30 higher than that in an isoviscous medium on the basis of these results the core formation time for the earth could be as little as 30 ma

delayed cooling of the earth s mantle due to variable thermal conductivity and the formation of a low conductivity zone abstract the thermal conductivity of mantle materials decreases with higher temperatures and increases with greater pressure due to phonon mechanism but increases with temperature for radiative transfer this trade off attribute allows for the formation of a low conductivity zone lcz within the top thermal boundary layer in mantle convection we have studied with a two dimensional 2 d cartesian model the potential of this low conductivity zone in retarding secular cooling of the mantle for a longer period of time than models with constant thermal conductivity using a recently proposed model for thermal conductivity and an adiabatic boundary condition for the bottom of the mantle we have carried out a set of numerical experiments within the framework of the extended boussinesq approximation for constant viscosity depth dependent thermal expansivity and variable thermal conductivity with surface rayleigh numbers between around 106 and around 107 we have employed internal heating between two and four times the chondritic level and half life time values of 2 5 ga and 5 ga the cooling rate of the mantle can be decreased by the feedback interaction between mantle conductivity and internal heating which gives rise to slower sinking cold currents the retardation time increases with the strength of radiogenic heating and can be as long as a couple of billion years for high initial heating rates four times the chondritic value however increasing the radiative contribution of the conductivity speeds up the cooling process the less the radiative contribution is the more mantle cooling would be retarded in the course of adiabatic cooling we find the paradoxical situation in which the effective rayleigh number of the mantle can actually increase with time we suggest then that because of the possibilities for the formation of low conductivity zones adjacent to the thermal boundary layers which bring forth unexpected consequences mantle thermal conductivity should be considered as a fundamentally important factor in constraining the thermal evolution of both the core and mantle

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

the interior structure of mars implications from snc meteorites two end member models of mars present interior structure are presented the first model is optimized to satisfy the geochemical data derived from the snc meteorites in terms of the bulk chondritic ratio fe si 1 71 while the second model is optimized to satisfy the most probable maximum value c 0 366 x m p r p 2 of the polar moment of inertia factor hydrostatic equilibrium and stationary heat transfer are assumed and the basic differential equations for the mechanical and thermal structure are solved numerically together with an isothermal murnaghan birch type equation of state truncated in eulerian strain at forth order we obtain the radial distribution of mass hydrostatic pressure gravity temperature and heat flow density along with the corresponding density stratification viscosity profiles and the global seismic velocity structure of model mars the first model being consistent with the geochemical requirement produces c 0 357 x m p r p 2 whereas the second model commensurate with the geophysical constraint gives fe si 1 35 the calculated central pressure is about 40 gpa in both models and the central temperature is in the 2000 to 2200 k range the model calculations suggest a fe ni fes core a little less than one half of the planetary radius in size surrounded by a silicate mantle subdivided into lower spinel and upper olivine layers and overlain by a 100 to 250 km thick basaltic crust and a surface heatflow density of 25 to 30 mw m 2 in both models the pressure in the mantle is not sufficient for the spinel to perovskite transition to occur the present thermal lithosphere is estimated to be about 500 km thick and to be subdivided into a 300 km thick outermost rheological lithosphere and an underlying thermal boundary layer of mantle convection given the core sulfur content of 14 wt as derived from snc meteorites the martian core is found to be entirely molten implying the nonoperation of a self sustained dynamo due to the absence of sufficiently vigorous convection

a model of metal silicate separation on growing planets abstract the thermal evolution of planets during their accretionary growth is strongly influenced by impact heating the temperature increase following a collision takes place mostly below the impact location in a volume a few times larger than that of the impactor impact heating depends essentially on the radius of the impacted planet when this radius exceeds 1000 km the metal phase melts and forms a shallow and dense pool that penetrates the deep mantle as a diapir to study the evolution of a metal diapir we propose a model of thermo chemical readjustment that we compare to numerical simulations in axisymmetric spherical geometry and with variable viscosity we show that the metallic phase sinks with a velocity of order of a stokes velocity the thermal energy released by the segregation of metal is smaller but comparable to the thermal energy buried during the impact however as the latter is distributed in a large undifferentiated volume and the former potentially liberated into a much smaller volume the diapir and its close surroundings a significant heating of the metal can occur raising its temperature excess by at most a factor of 2 or 3 when the viscosity of the hot differentiated material decreases the proportion of thermal energy transferred to the undifferentiated material increases and a protocore is formed at a temperature close to that of the impact zone

palaeoclimate determination from cave calcite deposits calcite deposits formed in limestone caves have been found to be an excellent repository of palaeoclimatic data for terrestrial environments the very presence of a relict deposit indicates non glacial conditions at the time of formation and both 14c and uranium series methods can be used to date the deposit and hence the age of these climatic conditions variations in 13c and 18o content of the calcite in 2h and 18o content of fluid inclusions in trace element concentrations and more recently in pollen assemblages trapped in the calcite are all potentially available as synchronous palaeoclimatic indicators previous work has tended to concentrate mainly on abundance of deposits as a palaeoclimatic indicator for the last 300 000 years this literature is briefly reviewed here together with the theory and methods of analysis of the u series and stable isotopic techniques the combined use of u series ages and 13c and 18o variations in cave calcites illustrates the potential for palaeoclimate determination previously unpublished results of stable isotopic variations in dated calcites from caves in northern england indicate the level of detail of stable isotopic variations and time resolution that can be obtained and the complexity of interpretation that may arise tentative palaeoclimatic signals for the periods 90 125 ka and 170 300 ka are presented more comprehensive studies are needed in future work especially in view of the difficulty in obtaining suitable deposits and the ethics of cave deposits conservation