chondritic mn na ratio and limited post nebular volatile loss of the earth abstract the depletion pattern of volatile elements on earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks the processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de volatilization induced by heating and impacting during planetary accretion after the dispersion of the h2 rich nebular gas furthermore as many volatile elements are also siderophile metal loving it is often difficult to deconvolve the effect of volatility from core formation with the notable exception of the earth all the differentiated terrestrial bodies for which we have samples have non chondritic mn na ratios taken as a signature of post nebular volatilization the bulk silicate earth bse is unique in that its mn na ratio is chondritic which points to a nebular origin for the depletion unless the mn na in the bse is not that of the bulk earth be and has been affected by core formation through the partitioning of mn in earth s core here we quantify the metal silicate partitioning behavior of mn at deep magma ocean pressure and temperature conditions directly applicable to core formation the experiments show that mn becomes more siderophile with increasing pressure and temperature modeling the partitioning of mn during core formation by combining our results with previous data at lower p t conditions we show that the core likely contains a significant fraction 20 to 35 of earth s mn budget however we show that the derived mn na value of the bulk earth still lies on the volatile depleted end of a trend defined by chondritic meteorites in a mn na vs mn mg plot which tend to higher mn na with increasing volatile depletion this suggests that the material that formed the earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula and experienced limited post nebular volatilization

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

variable preservation of middle tertiary coarse grained nearshore to outer shelf storm deposits in southern california abstract the middle tertiary oligocene early miocene strata of the san emigdio range in southern california were deposited along a shoreline oriented north northeast to south southwest adjacent to a tectonically active highland that formed the southern margin of the san joaquin basin abundant storm deposits sandstone and conglomerate are preserved in the san emigdio pleito and lower temblor formations extensive lateral exposures allow recognition of fair weather and storm dominated facies in contemporaneous nearshore inner shelf and outer shelf deposits the nearshore deposits consist of coarse grained progradational sequences that are similar to those described by clifton 1981 in miocene rocks of the nearby caliente range each complete sequence consists of in ascending order a basal transgressive lag followed by inner shelf surf zone longshore trough and beach foreshore facies the inner shelf deposits consist of fair and foul weather deposits the former deposits comprise massive locally pebbly very fine grained sandstone whereas the latter deposits consist of alternating intervals of cross stratified landward oriented conglomerate and hummocky cross stratified fine grained sandstone the outer shelf deposits are composed of massive very fine grained to silty sandstone and sequences of mollusk beds and hummocky cros stratified sandstone the massive outer shelf sandstones were deposited during periods of dominantly fair weather the sequences of hummocky cross stratified sandstone were deposited during and immediately after storms the outer shelf storm deposits apparently were preserved on an event by event basis whereas the inner shelf storm deposits were preserved in amalgamated packages unmodified storm deposits are rare in the nearshore deposits owing to the reworking capabilities of high energy nearshore processes reconstructions of wave conditions based on airy wave theory paleogeographic constraints and storm facies suggest that peak storm waves were more than 5 m high with periods of 7 9 seconds the study area was situated at the end of a long fetch in a favorable position to receive the full brunt of northwesterly wind driven waves

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

magma ocean formation due to giant impacts current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts an important thermal consequence of such impacts is melting and formation of a large melt pond if the planet s isostatic adjustment time scale is short compared to the magma pond s cooling time scale the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth although a giant impact striking at 10 15 km s 1 deposits enough energy to melt the entire planet the distribution of that energy is important in determining the thermal outcome of the collision we examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths additionally we examine the effects of the planet s initial temperature on the generated melt volume the hugoniot curve plotted in pressure entropy space is used to determine the shock pressure required to completely melt the material for room temperature dunite this pressure is about 150 gpa and the partial melt region is narrow for dunite initially at the solidus temperature this pressure is about 115 gpa the partial melt region extends throughout the planet once the melting pressure is known an impact melting model based on the second hugoniot equation the linear shock particle velocity relationship and the empirical particle velocity distance relationship is used to estimate the radial distance melting occurred from the impact site once the distance is found the melt region s geometry determines the associated melt volume partial melt volume is also estimated the melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated the model is also used to estimate the fraction of a planet melted by the initial shock wave nominal conditions of the moon forming giant impact projectile planet mass 0 14 impact speed 15 km s 1 generate melting of 30 65 of the planet depending on its initial temperature whole planet melting requires projectile planet mass ratios of 0 4 for a 15 km s 1 impact if the planet was near its solidus before the impact isostatic relaxation may generate a significant volume of additional melting

porosity prediction prior to drilling in sandstones of the kekiktuk formation mississippian north slope of alaska porosity in sandstones of the kekiktuk formation was successfully estimated prior to drilling of the 1 leffingwell wildcat well north slope of alaska the estimate was based on a calibration dataset used to evaluate the effects of 1 framework grain composition 2 depositional facies and 3 postdepositional processes on porosity of kekiktuk sandstones the sandstones of the kekiktuk formation are chert bearing sublitharenites and quartzarenites characterized by a homogeneous composition of the detrital framework in the study area thus mineral composition is not a major factor responsible for differences in reservoir quality based on outcrop and available core observations the kekiktuk formation was interpreted to include several wet fan deltas the depositional model suggested that the 1 leffingwell well would penetrate the distal fine grained facies of one such system a petrographic study indicated that in fine and very fine grained kekiktuk sandstones such as those predicted in the wildcat porosity was reduced primarily by silica cementation silica cementation in turn is related to burial history because of the relationship among porosity silica cementation and burial history burial history diagrams provided a measure of the effect of burial history on porosity in available calibration wells a synthetic burial history curve was constructed prior to drilling of the 1 leffingwell well from available seismic data this burial history curve was then used to estimate the well s porosity based on the previously established porosity burial history relationship

physical state of an early magma ocean constrained by the thermodynamics and viscosity of iron silicate liquid abstract the initial cooling stage and crystallization of a magma ocean were significantly affected by the thermodynamics and viscosity of iron silicate liquid here we use first principles molecular dynamics based on density functional theory plus the hubbard u method to study the structures thermodynamics and viscosities of fe2sio4 liquid at 3000 6000 k under pressure conditions spanning the entire mantle our calculations show that the compressibility of fe2sio4 liquid is weakened at pressures above 50 gpa the densification of fe2sio4 liquid under compression is mainly manifested by a decrease in the distance among si o polyhedra and an increase in the cation anion coordination number we find that the viscosity of the fe2sio4 liquid has a positive pressure dependence and the effect of pressure on viscosity decreases with increasing temperature the predicted behaviour of viscosity coefficients of the fe2sio4 liquid at different p t conditions can be described well as p t exp 7 89 0 0042 p 0 0000632 p 2 3800 61 6 p 0 18 p 2 t 1000 compared to mg2sio4 liquid the viscosity of fe2sio4 liquid is lower under the pressure of the lower mantle along isotherms we calculate the adiabat of the fe2sio4 liquid in a magma ocean and the results show that the iron content has little effect on the adiabats of mg fe 2sio4 liquid in the magma ocean combining our calculated thermodynamic properties and viscosities with those of previous studies the physical properties of an early magma ocean were constrained the upper bound of the potential temperature for magma ocean crystallization is 3250 k we constructed the range of the viscosity profile of a magma ocean and found that the lower viscosity of iron rich silicate liquid would maintain the viscosity of an early magma ocean in the range of several mpa s as the magma ocean starts to crystallize the lower bound of the viscosity at the surface and the core mantle boundary are 0 0020 pa s and 0 0068 pa s respectively the weakening of the viscosity of the iron silicate liquids would have a significant impact on the evolution of the magma ocean

structural features and formation conditions of mud diapirs in the andaman sea basin data from offshore oil and gas explorations have revealed that mud diapirs occur widely not only at continental margins but also in foreland basins and may have played an important role in the entrapment of oil and gas although the structural features and formation mechanism of salt diapirs have been extensively investigated mud diapirs are still not fully understood largely due to the difficulty of identifying them from seismic data in this paper the structural features and main controlling factors of mud diapirs in the andaman sea basin are investigated based on seismic profiles combined with drilling data and regional tectonic settings the results show that there are five types of mud diapir in the andaman sea basin turtleback mud diapir mud dome piercing mud diapir mud volcano and gas chimney like mud diapir turtleback mud diapirs mainly occur in the southern segment of the accretionary wedge of the andaman sea basin which is far from the bengal fan and characterized by low deposition rate and strong compression tectonic setting piercing mud diapirs exist mainly in the central segment of the accretionary wedge which is close to provenances of sediments and characterized by rapid sedimentation rates large mudstone thickness and transpressional tectonic setting mud domes and mud volcanoes mainly occur in the northern segment of the accretionary wedge which is characterized by rapid sedimentation rates large mudstone thickness and sedimentary wedge growth tectonic setting the gas chimney like mud diapirs only occur in the northern segment of the back arc depression close to the sagaing strike slip fault belt which is characterized by high deposition rate large mudstone thickness and high geothermal gradient these features suggest that thick mudstone deposit rapid sedimentation rates large geothermal gradient strong tectonic stress and gravitational spreading and sliding may have prompted the formation of mud diapirs in the andaman sea basin

turbulent mixing of metal and silicate during planet accretion and interpretation of the hf w chronometer in the current view of planet formation the final assembly of the earth involved giant collisions between proto planets 1000 km radius with the moon formed as a result of one such impact at this stage the colliding bodies had likely differentiated into a metallic core surrounded by a silicate mantle during the moon forming impact nearly all metal sank into the earth s core we investigate to what extent large self gravitating iron cores can mix with surrounding silicate and how this influences the short lived chronometer hf w used to infer the age of the moon we present fluid dynamical models of turbulent mixing in fully liquid systems attempting to place constraints on the degree of mixing erosion of sinking cores driven by rayleigh taylor instability does lead to intimate mixing and equilibration but large blobs 10 km diameter do not emulsify entirely emulsification is enhanced if most of the accreting metal cores deform into thin structures during descent through the earth s mantle yet only 1 20 of earth s core would equilibrate with silicate during earth s accretion the initial speed of the impactor is of little importance we proceed to evaluate the mixing potential for shear instabilities where silicate entrainment across vertical walls causes mixing the turbulent structure indicates that vortices remain at the largest scale and do not mix to centimeter length scale where diffusion operates and isotopes can equilibrate thus incomplete emulsification and equilibration of accreting iron cores is likely to occur the extent of metal silicate equilibration provides key information for interpretation of siderophile budgets and the timing of core formation using the hf w chronometer the time scale of core formation derived from the hf w chronometer is usually tied to the last major metal silicate re equilibration believed to coincide with time of the moon forming impact however we show that large cores have limited ability to reset the hf w system in the silicate earth excess 182 w in bulk silicate earth is more sensitive to early core formation processes than to radiogenic ingrowth after the last giant impact

fluid dynamics of local martian magma oceans the evolution of a melt region produced by a large impact during mars formation is addressed while some impact induced melt is redistributed during crater excavation sufficiently large impacts much larger than basin forming impacts generate an intact melt region which is retained beneath the excavation zone i e a local magma ocean local magma ocean evolution depends on the effective rheology controlling large scale deformation of the solid part of the planet mechanism of crystallization and melt region size within the uncertainties of various parameters two scenarios are possible for sufficiently weak rheology or large melt region size evolution is characterized by rapid extrusion and formation of a global magma ocean for sufficiently strong rheology or small melt region size in situ crystallization to a partially molten solid state occurs prior to isostatic adjustment subsequent to in situ crystallization local magma ocean evolution depends on melt region size and efficiency of lateral redistribution compared to bulk conductive cooling for large melt regions lateral spreading occurs via plastic deformation and results in an asymmetric global partial melt layer for small melt region size viscous spreading viscous can result in bulk cooling below the solidus prior to formation of a global layer a hypothesis for the origin of the hemispherical crustal dichotomy and tharsis rise is suggested the dichotomy is associated with a global partial melt layer produced by evolution of a large local magma ocean after dichotomy formation evolution of a second smaller local magma ocean is related to tharsis development

turbulent metal silicate mixing fragmentation and equilibration in magma oceans abstract much of the earth was built by high energy impacts of planetesimals and embryos many of these impactors already differentiated with metallic cores of their own geochemical data provide critical information on the timing of accretion and the prevailing physical conditions but their interpretation depends critically on the degree of metal silicate chemical equilibration during core mantle differentiation which is poorly constrained efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal silicate mass transfer here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment with fragmentation into droplets eventually resulting from the entrainment process in our experiments fragmentation of the dense fluid occurs after falling a distance equal to 3 4 times its initial diameter at which point a sizable volume of ambient fluid has already been entrained and mixed with the dense falling fluid contrary to previous assumptions we demonstrate that fragmentation of the metallic phase into droplets may not be required for efficient equilibration turbulent mixing by drastically increasing the metal silicate interfacial area may result in fast equilibration even before fragmentation efficient re equilibration is predicted for impactors of size small compared to the magma ocean depth in contrast much less re equilibration is predicted for large impacts in situations where the impactor core diameter approaches the magma ocean thickness

laboratory experiments on the breakup of liquid metal diapirs the validity of the iron rain scenario i e the widely accepted model for the dynamics of iron sedimentation through a magma ocean during the latest stage of the earth s accretion is explored via a suite of laboratory experiments liquid gallium and mixtures of water and glycerol are used as analogs of the iron and the molten silicate respectively this allows us to investigate the effects of the viscosity ratio between iron and silicate and to reproduce the relevant effects of surface tension on the fragmentation dynamics while the classical iron rain scenario considers a population of purely spherical drops with a single characteristic radius that fall towards the bottom of the magma ocean at a unique velocity without any further change our experiments exhibit a variety of stable shapes for liquid metal drops a large distribution of sizes and velocities and an intense internal dynamics within the cloud with the superimposition of further fragmentations and merging events our results demonstrate that rich and complex dynamics occur in models of molten metal diapir physics further we hypothesize that the inclusion of such flows into state of the art thermochemical equilibration models will generate a similarly broad array of complex and likely novel behaviors

detachment folds with fixed hinges and variable detachment depth northeastern brooks range alaska abstract detachment anticlines in the northeastern brooks range accommodated displacement above a detachment by buckling of a competent unit over an incompetent unit meso and microstructures in hinges and a lack of relict hinge structures in limbs suggest that these folds grew with fixed hinges the structural thickness of the incompetent unit beneath the folds detachment depth varies from less than to greater than the stratigraphic thickness a model in which incompetent unit thickness varies with fold area better approximates the geometry of the folds than does a more conventional constant depth model additional discrepancies between modelled and observed incompetent unit thickness and field observations suggest non plane strain and or transport of material through the boundaries of the fold in the plane of the cross section the results of this study suggest a typical evolutionary sequence for detachment folds in the northeastern brooks range which may be applicable elsewhere anticlines initiate as fixed hinge buckle folds rapid initial increase in anticlinal cross sectional area results in a decrease in incompetent unit thickness fold area begins to decrease with tightening beyond an interlimb angle of 90 dg decreasing fold area is accommodated through some combination of structural thickening of the incompetent unit transport of solid or dissolved material out of the plane of section transport of material through the boundaries of the fold in the plane of the cross section and or truncation by thrust faults

experiments on fragmentation and thermo chemical exchanges during planetary core formation abstract the initial thermo chemical state of telluric planets was largely controlled by mixing following the collision of differentiated proto planets up to now most models of planet formation simply assume that the iron core of the impactors immediately broke up to form an iron rain within a large scale magma ocean leading to the rapid equilibration of the whole metal with the whole mantle only recent studies have focused on resolving the fluid mechanics of the problem with the aim to define more relevant diffusion advection models of thermal and chemical exchanges within and between the two fluids furthermore the influence of the viscosity ratio on this dynamical process is generally neglected whilst it is known to play a role in the breakup of the initial iron diapirs and in the shape of the resulting droplets here we report the results of analog laboratory experiments matching the dynamical regime of the geophysical configuration high speed video recording allows us to describe and characterize the fluid dynamics of the system and temperature measurements allow us to quantify the diffusive exchanges integrated during the fall of the liquid metal we find that the early representation of this flow as an iron rain is far from the experimental results the equilibration coefficient at a given depth depends both on the initial size of the metal diapir and on the viscosity of the ambient fluid whereas the falling speed is only controlled by the initial size various scalings for the diffusive exchanges coming from the literature are tested we find good agreement with the turbulent thermal model developed by deguen et al 2014

iron isotope fractionation during supergene weathering process and its application to constrain ore genesis in gaosong deposit gejiu district sw china abstract fe isotope compositions of bulk samples from gaosong ore deposit in gejiu district sw china were investigated and an overall variation in 56 fe values from 0 33 to 0 20 has been observed in this study the 56 fe values of primary sulfide ores are lower than the oxidized ores while the iron isotope compositions of gossan samples which represent highest oxidation degree are heavier than the oxidized ore samples these data indicate that iron isotopes experienced fractionation during supergene weathering process furthermore heavier iron isotopes enriched in more oxidized products another highlight is the fe isotope compositions that are affected by mineralogy which is considered as the primary mechanism of the large fe isotopic variations in the primary ores enrichment of light iron isotopes in primary sulfide ores suggests that iron isotopes fractionated during fluid exsolution from its parental magma and the fe source of skarn ores is mainly the magmatic source this observation that significant fe isotope fractionation occurs in supergene weathering process and fluid exsolution process provides an example in using fe isotopes to trace supergene geochemical cycling and ore deposit formation evolution processes

hydrological changes and holocene climate variations in nw china inferred from lake sediments of juyanze palaeolake by factor analyses abstract the eastern juyanze palaeolake in hyperarid north western china 41 75 42 n 101 5 102 e provides evidence of a complex hydrological pattern during the holocene multivariate statistics based on lithological geochemical and mineral data from the reference site g36 in the centre of the lake were performed to reconstruct the interrelation between lake hydrology and climate variability of the last 11 000 yr principal component analyses pca analyses enabled us to extract the three system variables runoff lake level water budget and salinity as the major factors which have influenced the lake history during a highly variable holocene climate we can also demonstrate that the independent variable total organic carbon toc is not only a function of bio productivity in lakes under warm wet climate conditions but more frequently related to surface runoff processes which can result in over estimation of pollen types used for climate reconstructions a combined consideration of all system variables with lithological parameters catchment characteristics and the local groundwater situation show that lake formation and its persistence strongly depended on local rainfall runoff and the status of the underlying aquifer our results indicate remarkable differences between the early holocene and mid to late holocene lake formation owing to changes in the aquifer system beneath the lake at about 10 700 cal bp freshwater lake formation starts with extreme runoff events under a wet climate repeated dry climate spells of reduced runoff the overall climate during the early holocene points to wet conditions with frequent phases of very high runoff and highest lake levels until about 8900 cal bp extremely low runoff occurred between 8900 and 8100 cal bp indicating already dry climate conditions some hundred years prior to the worldwide recorded responses of the 8 2 ka cold dry event a second period of major dry climate conditions with generally low but fluctuating runoff unstable water budget and deposition of aeolian sand lasted for about 2100 yr between 7500 and 5400 cal bp these climate conditions corroborate previous assumptions of a mid holocene dry period in arid north western china increased runoff after 5400 cal bp under wet climate conditions led to a complete refill of the aquifer at about 5000 cal bp and favoured the development of a saline lake for about 3500 yr in terms of hydrology the time between 5400 and 4000 cal bp appears to be the climate optimum compared with the early holocene wet climate the mid to late holocene local rainfall was less pronounced and displays a general decreasing trend towards complete desiccation of the lake our results indicate an extremely variable moisture availability in arid regions of north western china during the entire holocene owing to the interplay of the east asian summer monsoon with the westerly waves at the boundary of the summer monsoon limit variations from dry to wet climate conditions seem to have been more pronounced than in other monsoon regions of china

characteristics of coarse grained sequences deposited in nearshore wave dominated environments examples from the miocene of south west oregon the conglomeratic sandstone of the sandstone of floras lake miocene is a superbly exposed example of a coarse grained sequence deposited in a high energy storm wave dominated shallow marine environment the features of the unit suggest deposition on a shoreface in proximity to a fluvial source distinguishing characteristics include amalgamated hummocky stratified sandstone low angle cross stratified conglomerate beds lenticular conglomerate beds tabular conglomerate beds high angle scours trough cross bedded sandstone organic rich beds and burrows of several sizes these features are interpreted in terms of their depths of deposition generation by fair weather storm and or flood processes and as indicators of relative rates of sedimentation the unit records complex interaction of tectonic wave fluvial and tidal processes relative depth changes indicated in the sequence probably reflect changes in the balances between sediment supply basin subsidence and eustatic sea level changes wave processes are manifest in the presence of structures deposited both above and below fair weather wave base deposition and reworking by chaotic seas associated with local storms and by long period swell associated with distant storms may be indicated by the interbedding of amalgamated hummocky stratified sandstone and conglomerate beds the effects of the lateral migration of a fluvial source with time are reflected by the changing nature and apparent rates of supply of sediments deposited in the nearshore zone tidal processes are manifest largely as superimposed features on wave and current generated structures biogenic structures are an important clue to the rates and frequencies of all these processes the conglomeratic sandstone was deposited on a high energy tectonically active continental margin similar to the present setting of the southern oregon coast it was deposited at varying depths in a subsiding basin during a time of world wide sea level rise the sequence provides an opportunity for the study of coarse grained nearshore marine sediments and the delineation of the interaction of various processes during deposition detailed sedimentologic and palaeoecologic analysis provides insight into the nature of storm and flood processes that are difficult to observe in the modern environment

differentiated planetesimal impacts into a terrestrial magma ocean fate of the iron core abstract the abundance of moderately siderophile elements iron loving e g co ni in the earth s mantle is 10 to 100 times larger than predicted by chemical equilibrium between silicate melt and iron at low pressure but it does match expectation for equilibrium at high pressure and temperature recent studies of differentiated planetesimal impacts assume that planetesimal cores survive the impact intact as concentrated masses that passively settle from a zero initial velocity and undergo turbulent entrainment in a global magma ocean under these conditions cores greater than 10 km in diameter do not fully mix without a sufficiently deep magma ocean we have performed hydrocode simulations that revise this assumption and yield a clearer picture of the impact process for differentiated planetesimals possessing iron cores with radius 100 km that impact into magma oceans the impact process strips away the silicate mantle of the planetesimal and then stretches the iron core dispersing the liquid iron into a much larger volume of the underlying liquid silicate mantle lagrangian tracer particles track the initially intact iron core as the impact stretches and disperses the core the final displacement distance of initially closest tracer pairs gives a metric of core stretching the statistics of stretching imply mixing that separates the iron core into sheets ligaments and smaller fragments on a scale of 10 km or less the impact dispersed core fragments undergo further mixing through turbulent entrainment as the molten iron fragments rain through the magma ocean and settle deeper into the planet our results thus support the idea that iron in the cores of even large differentiated planetesimals can chemically equilibrate deep in a terrestrial magma ocean

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

experiments on turbulent metal silicate mixing in a magma ocean we compare the results of laboratory fluid dynamics experiments with theoretical models of turbulent entrainment in two phase buoyant plumes and thermals to estimate the amount of mixing between the iron core of a planetesimal or planetary embryo and the molten silicates in a magma pool formed by its impact with a growing planet during accretion we demonstrate experimentally that turbulent plumes in immiscible fluids fragment into droplets and that the envelope of the droplet distribution is indistinguishable from the envelope of a turbulent plume in a single phase fluid under the same dynamical conditions implying that turbulent entrainment concepts are applicable to immiscible fluids mixing a series of experiments are made on the time evolution of a two phase turbulent thermal representing a planetesimal core falling under its own negative buoyancy in a spherical fluid representing an impact produced magma pool two stages of mixing are observed in these experiments the first corresponding to turbulent entrainment during free fall of the thermal the second corresponding to entrainment in turbulent gravity currents that form after the thermal reaches the base of the magma pool we demonstrate that the amount of mixing between metals and silicate liquids in a magma pool depends on the rouse number of the metal fragments and increases rapidly with the radius of the proto planet we derive a similarity model for metal silicate mixing in a spherical magma pool assuming a constant entrainment coefficient for the turbulent liquid metal phase this model supports our experimental finding that a small metal core of an impactor will become diluted i e mix within a deep magma pool but a large impacting core will not fully dilute before reaching the base of the magma pool

a review of wave dominated clastic shoreline deposits abstract barrier islands beaches wave dominated deltas and chenier plains probably form more than one fifth of present coasts and constitute an even larger proportion of the subsiding lowland coasts likely to be preserved in the stratigraphic record the geometry vertical sequences and composition of their deposits are the result of 1 shoreline behaviour whether transgressive regressive or stable 2 physical processes particularly the relative intensities of waves and tides 3 climate 4 global tectonic setting and 5 topography of underlying deposits published interpretations indicate that equivalent deposits are abundant in the geological record sandstones are mostly quartzose cemented by carbonates and quartz and have sheet or linear geometries ancient deposits can provide evidence of palaeogeography and some are economically significant particularly as hydrocarbon reservoir rocks four end member sedimentation models are proposed for the interpretation of ancient deposits 1 transgressive sheet sands associated with deltas 2 non deltaic transgressive sheet sands 3 regressive sheet sands and 4 linear sand bodies probable depositional settings geometries characteristics of deposits and palaeocurrent patterns are discussed

the deep earth may not be cooling down abstract the earth is a thermal engine generating the fundamental processes of geomagnetic field plate tectonics and volcanism large amounts of heat are permanently lost at the surface yielding the classic view of the deep earth continuously cooling down contrary to this conventional depiction we propose that the temperature profile in the deep earth has remained almost constant for the last 4 3 billion years the core mantle boundary cmb has reached a temperature of 4400 k in probably less than 1 million years after the moon forming impact regardless the initial core temperature this temperature corresponds to an abrupt increase in mantle viscosity atop the cmb when 60 of partial crystallization was achieved accompanied with a major decrease in heat flow at the cmb then the deep earth underwent a very slow cooling until it reached 4100 k today this temperature at or just below the mantle solidus is suggested by seismological evidence of ultra low velocity zones in the d layer such a steady thermal state of the cmb temperature excludes thermal buoyancy from being the predominant mechanism to power the geodynamo over geological time an alternative mechanism to sustain the geodynamo is mechanical forcing by tidal distortion and planetary precession motions in the outer core are generated by the conversion of gravitational and rotational energies of the earth moon sun system mechanical forcing remains efficient to drive the geodynamo even for a sub adiabatic temperature gradient in the outer core our thermal model of the deep earth is compatible with an average cmb heat flow of 3 0 to 4 7 tw furthermore the regime of core instabilities and or secular changes in the astronomical forces could have supplied the lowermost mantle with a heat source of variable intensity through geological time episodic release of large amounts of heat could have remelted the lowermost mantle thereby inducing the dramatic volcanic events that occurred during the earth s history in this scenario because the moon is a necessary ingredient to sustain the magnetic field the habitability on earth appears to require the existence of a large satellite

heterogeneous delivery of silicate and metal to the earth by large planetesimals after the moon s formation earth experienced a protracted bombardment by leftover planetesimals the mass delivered during this stage of late accretion has been estimated to be approximately 0 5 of earth s present mass based on highly siderophile element concentrations in the earth s mantle and the assumption that all highly siderophile elements delivered by impacts were retained in the mantle however late accretion may have involved mostly large 1 500 km in diameter and therefore differentiated projectiles in which highly siderophile elements were sequestered primarily in metallic cores here we present smoothed particle hydrodynamics impact simulations that show that substantial portions of a large planetesimal s core may descend to the earth s core or escape accretion entirely both outcomes reduce the delivery of highly siderophile elements to the earth s mantle and imply a late accretion mass that may be two to five times greater than previously thought further we demonstrate that projectile material can be concentrated within localized domains of earth s mantle producing both positive and negative 182w isotopic anomalies of the order of 10 to 100 ppm in this scenario some isotopic anomalies observed in terrestrial rocks can be explained as products of collisions after moon formation

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

application of the tectono geochemistry method to mineral prospectivity mapping a case study of the gaosong tin polymetallic deposit gejiu district sw china abstract the tectono geochemistry method as a lithogeochemical exploration tool is a process centric approach based on the premise that element migration and concentration within and adjacent to geological structures are controlled by large scale dynamic earth processes that operate on a variety of scales to focus mass and energy flux here we present a case study of the gaosong tin polymetallic deposit gejiu district sw china illustrating how the tectono geochemistry method can be applied to mineral prospectivity mapping as a first step 2216 fault rock samples collected within the geiju district were assayed followed by a detailed examination of the assay results by means of factor analysis and multifractal singularity mapping the main aims of these analyses were to 1 statistically explore the data with respect to specific element concentrations associations and geochemical patterns by which the fault rock samples can be grouped 2 better characterize the samples in terms of whether or not the rocks recorded any evidence for hydrothermal mineralization processes and 3 identify any geochemical anomalies that may present vectors to buried ore the results illustrate that element distribution patterns are greatly influenced by fault permeability and that ne sw striking faults are the most favorable in terms of concentration of ore elements factor analysis greatly assisted the identification and interpretation of for example element associations and geochemical zonation patterns genetically related to intrusions recognition of singularities was of particular importance with respect to identifying and delineating primary fault tectono geochemical anomalies that may be caused by buried ore of particular interest are low singularity values as these correspond with positive geochemical anomalies over known ore deposits in the gejiu district anomalies delineated by local singularity exponents may represent undiscovered ore and thus warrant further exploration

numerical modeling of fault controlled fluid flow in the genesis of tin deposits of the malage ore field gejiu mining district china a distinct element finite difference model based on geologic data from the tin polymetallic hydrothermal deposits of malage is constructed to simulate the geologic processes of fault controlled fluid migration during hydrothermal ore genesis the history of hydrothermal ore genesis is strongly affected by the interaction between fault deformation and fluid flow an injected fluid induces fault slip by lowering the effective stress across a fault the subsequent movement on the fault enhances the fault aperture which provides a channelway that both facilitates and focuses fluid flow the variation of fluid injection under certain stress conditions causes cyclic movement on faults this cyclic failure gives rise to pulsating fluid flow along the faults which may be responsible in part for the precipitation zoning of mineral deposits as an important structural condition for ore formation in any fault related mineralized region like malage the linking up of fracture networks not only allows appropriate long distance channels for fluid migration but also provides the appropriate conditions for ore deposition at particular structural sites this study indicates that different fluid flow patterns i e changes in fluid flow rate or velocity with time and space can reflect the variation of structural environment for instance the flow velocity is increased gradually over time on the relatively connected faults such as the northwest southeast trending fault and the western half of the east west trending yuanlao fault in the center of the malage ore field these are the main pathways for the ore forming fluids in the smaller secondary faults the flow velocity fluctuates more rapidly with time and space in some instances causing conditions that are favorable to mineral deposition the main ore deposition sites occur on the smaller secondary faults the detailed variation of fluid and aperture conditions modeled in this complex fault array can be related to the formation and location of mineral deposits both predictively and conceptually the modeling also demonstrates that the fault deformation and fluid flow are sensitive to the principal stress orientation if the orientation of sigma 1 is changed by more than 15 degrees there are very different results for the calculated fault motion pattern hydraulic aperture and fluid flow

compositional and thermal equilibration of particles drops and diapirs in geophysical flows core formation crystal melt separation mingling of immiscible magmas and diapirism are fundamental geological processes that involve differential motions driven by gravity diffusion modifies the compo sition or and temperature of the considered phases while they travel solid particles liquid drops and viscous diapirs equilibrate while sinking rising through their surroundings with a time scale that depends on the physics of the flow and the material properties in particular the internal circulation within a liquid drop or a diapir favors the diffusive exchange at the interface to evaluate time scales of chemical thermal equilibration between a material falling rising through a deformable medium we propose analytical laws that can be used at multiple scales they depend mostly on the non dimensional peclet and reynolds numbers and are consistent with numerical simulations we show that equilibration between a particle drop or diapir and its host needs to be considered in light of the flow structure complexity it is of fundamental importance to identify the dynamic regime of the flow and take into account the role of the inner circulation within drops and diapirs as well as inertia that reduces the thickness of boundary layers and enhances exchange through the interface the scaling laws are applied to predict nickel equilibration between metals and silicates that occurs within 130 m of fall in about 4 minutes during the metal rain stage of the earth s core formation for a mafic blob 10 cm diameter sinking into a felsic melt trace element equilibration would occur over 4500 m and in about 3 years

compositional data analysis in the study of integrated geochemical anomalies associated with mineralization abstract geochemical data are typical compositional data which should be opened prior to univariate and multivariate data analysis in this study a frequency based method robust principal component analysis rpca and a frequency space based method spectrum area fractal model s a are applied to explore the effects of the data closure problem and to study the integrated geochemical anomalies associated with polymetallic cu mineralization using a stream sediment geochemical dataset collected from the zhongteng district fujian province china the results show that 1 geochemical data should be opened prior to rpca to avoid spurious correlation between variables 2 geochemical pattern is a superimposition of multi processes and should be decomposed and 3 the s a fractal model is a powerful tool for decomposing the mixed geochemical pattern

direct numerical simulation of an iron rain in the magma ocean core formation in terrestrial planets is a complex process possibly involving several mechanisms this paper presents a direct numerical simulation of one of these the separation of an emulsion of metal in a magma ocean the model using a fully lagrangian approach called the moving particle semi implicit method solves the equations of fluid dynamics including a proper treatment of surface tension it allows investigation of the balances controlling the distribution of drop size and velocity in both two and three dimensional situations a scaling analysis where buoyancy is balanced by both surface tension and inertia correctly predicts the average values in these quantities the full calculation gives an average drop radius of 1 5 cm falling at a velocity of about 30 cm s 1 analysis of the full distribution remains interesting and shows that a significant part of the smallest droplets is entrained upward by the return flow in molten silicate and might be entrained by succeeding thermal convection in addition we investigate the conversion of gravitational energy into viscous heating and the thermal equilibration between both phases we find that viscous heating is essentially produced at the surface of iron drops and that thermal equilibration is dominated by advection scaling thermal diffusion to chemical diffusion leads to the estimation that the latter would happen in less than 100 m in the magma ocean

braidplain evolution in the pennsylvanian south bar formation sydney basin nova scotia canada abstract the south bar formation is a 1 km thick alluvial succession in the pennsylvanian morien group of the sydney basin nova scotia that fines upward from conglomerate to pebbly sandstone to sandstone facies assemblages the conglomerate assemblage comprises mainly massive to horizontally stratified conglomerate and planar cross stratified sandstone attributed to deposition in proximal braided rivers confined between bedrock ridges the sandstone assemblage shows uniformity of facies and paleocurrents across the basin and is interpreted as a distal braidplain deposit the pebbly sandstone assemblage is transitional between the other two both sandstone assemblages are dominated by trough cross stratified sandstone formed by dune migration in channel tracts about 4 m deep this succession differs markedly from platte river and icelandic sandy braidplain deposits which are mainly planar cross stratified sands formed by broad shallow flow the south bar sandstones are more like south saskatchewan river deposits but differ in 1 greater abundance of trough sets and 2 rarity of planar sets and other components of shallow water channel fill these features are ascribed to 1 inheritance of relatively deep channels from confined upstream reaches 2 maintenance of deep flow in active tracts by local confinement between temporary banks and 3 rapid avulsive abandonment of active tracts which inhibited development of channel fill sequences evidence for local temporary confinement is preserved as in situ and slumped channel margin mudrock units lateral and vertical transitions from the upper south bar formation to the mud rich waddens cove and sydney mines formations are ascribed to changes in channel pattern from braided to meandering the former is attributed to decreased slope the latter to eustatic rise in sea level

early carboniferous transgression on a passive continental margin deposition of the kekiktuk conglomerate northeastern brooks range alaska the base of the ellesmerian sequence in the northeastern brooks range is a widespread terrigenous clastic succession assigned to the kekiktuk conglomerate late tournaisian visean the kekiktuk is situated above a regional angular unconformity and is the base of a transgressive succession that is thought to record coastal onlap associated with the formation of a passive continental margin six depositional units have been recognized in the kekiktuk conglomerate unit a consists of clast supported and rare matrix supported pebble and cobble conglomerate with minor interbeds of pebbly sandstone it records deposition at the base of incised paleovalleys from high sediment concentration flows and debris flows units b c and d consist of multistory fining upward cycles that record deposition within incised paleovalleys from low sinuosity bed load dominated streams low to moderate sinuosity bed load dominated streams and high sinuosity mixed load streams respectively unit e consists of multistory fining upward cycles and laminated sandstone with thin conglomerate stringers it records deposition in the distal regions of incised paleovalleys in a variety of marginal mari e settings including fluvial channel channel mouth bar beach ridge and coastal swamp environments unit f consists of horizontally bedded sandstone interbedded sandstone and organic rich mudstone it records deposition over paleotopographic highs on the sub mississippian unconformity from sheetfloods and in associated coastal swamp and mud flat settings relative sea level rise is thought to have initiated fluvial deposition in the northeastern brooks range by the latest tournaisian earliest visean coal bearing fluvial channel fill and flood basin successions and palynologic data suggest that this part of arctic alaska was situated in a humid climatic zone during the early carboniferous the stratigraphic and sedimentologic organization of the kekiktuk conglomerate indicates that once base level rise began to affect the northeastern brooks range local and regional variations in paleotopography along the sub mississippian unconformity exerted primary control on accommodation and consequent distribution of kekiktuk depositional environments the stratigraphic position of the kekiktuk conglomerate above a regional angular unconformity nd below marginal marine and shallow marine shales combined with its limited thickness widespread distribution and suite of paleoenvironments suggests deposition in an upland region situated landward of the tectonic hinge zone along a steadily subsiding passive continental margin thermal subsidence combined with eustatic sea level rise were probably responsible for relative sea level rise in arctic alaska and the resulting regional transgression end page 679

mapping of prospectivity and estimation of number of undiscovered prospects for lode gold southwestern ashanti belt ghana in the southwestern part of the ashanti belt the results of fractal and fry analyses of the spatial pattern of 51 known mines prospects of mostly lode gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales intersections of nne and nw trending faults were likely predominantly involved in local scale structural controls on lode gold mineralisation whilst nne trending faults were likely predominantly involved in district scale structural controls on lode gold mineralisation the results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area the applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines prospects results in a one level prediction of 37 undiscovered lode gold prospects the applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines prospects result in an estimate of 40 undiscovered lode gold prospects the study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits

evolution of thought on passive continental margins from the origin of geosynclinal theory 1860 to the present most of the current views on the evolution of passive margins have roots in ideas that were developed before 1930 in the context of continental drift and geosynclinal theory these ideas include the concept of an atlantic type of margin formed by rifting and continental drift the presence of a thick sedimentary deposit beneath the continental shelves and subsidence in response to such mechanisms as crustal thinning igneous underplating thermal contraction flexure and sediment loading as large amounts of new surface and subsurface data were acquired from modern passive margins after world war ii owing to significant advances in technology for geological and geophysical exploration of the ocean basins these early ideas were strengthened and modified with the development of plate tectonic theory the origin of passive margins as rifted trailing edges of continents became widely accepted and significant changes in thinking involved the role of passive margins and their implications for large horizontal displacements in the evolution of geosynclines within the past decade a large number of geophysical models have been developed for passive margins that focus once again on the problem of the mechanisms of vertical movements of the earth9s crust at the same time new developments in the acquisition and processing of data from ocean basins especially deep reflection data have resulted in major new concepts about the deep structure of passive margins including recognition of the importance of underplating and plutonic activity in the thinned rifted crust and the unexpected degree of faulting and formation of horizontal reflectors in the lower continental crust and subcrustal lithosphere

cool water carbonates in a paleoequatorial shallow water environment the paradox of the auernig cyclic sediments upper pennsylvanian carnic alps austria italy and its implications distinct parts of limestones within the upper paleozoic auernig group of the carnic alps austria and italy are characteristic of cool water carbonates the carnic alps were between 5 n and 10 s paleolatitude during the late carboniferous a position confirmed by dasyclad algae and fossil plants the floral association occurrence of coal seams and absence of evaporites indicate a humid tropical environment the entire section lacks abiotic components of typical warm water limestones no ooids and no aggregates occur within the auernig group parts of the limestones show surprisingly a cool water association of high diversity bryozoans brachiopods crinoids red algae sponge spicules and entomozoan ostracodes the genesis of these limestones atypical for a paleoequatorial setting cannot be explained by changes in salinity bathymetry or terrigenous input the water temperature possibly linked with upwelling nutrient supply and paleoceanographic currents is the most convincing cause of this unusual association paleoceanographic changes are interpreted as linked to contemporaneous glaciation deglaciation cycles in gondwana this paper shows that cool water carbonates in shallow water environments are not necessarily nontropical as generally interpreted future studies should consider water temperature oceanic circulation and availability of nutrients supplementary to bathymetry salinity and latitude related climate in interpretation of carbonate components

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

a comparison study of the c a and s a models with singularity analysis to identify geochemical anomalies in covered areas abstract fractal multifractal modeling of geochemical data is an interesting topic in the field of applied geochemistry identification of weak anomalies for mineral exploration in covered areas is one of the most challenging tasks for utilization of geochemical data in this study three fractal models consisting of the concentration area c a spectrum area s a and singularity index models were applied to identify geochemical anomalies in the covered area located in the chaobuleng fe polymetallic district inner mongolia china the results show that 1 the grassland cover weakens the concentrations of geochemical elements 2 the c a model has a limitation to identify weak anomalies in covered areas 3 the s a model is a powerful tool to decompose mixed geochemical patterns into a geochemical anomaly map and a varied geochemical background map but suffers edge effects in an irregular shaped study area and 4 the singularity index is a useful tool to identify weak geochemical anomalies

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

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

heat partitioning in terrestrial planets during core formation by negative diapirism article i nfo we investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets we model the dynamic evolution of an iron diapir sinking through a solid silicate proto mantle our calculations include viscous heating and strong temperature and composition dependence of viscosity we show that the diapir mean temperature evolves towards an asymptotic value td which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings and on the viscous rheology we derived a simple analytic model that captures the thermal evolution observed in our numerical experiments this model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs during their growth and early differentiation we show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs a large number of small sinking iron diapirs favors metal silicate heat exchange and leads to a relatively hot core which allows a sustainable dynamo as on earth a small number of large diapirs have the opposite effect and could correspond to a mars like planet with an early dynamo that is no longer active in all cases negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part which could trigger large amounts of melting in the early deep mantle

a re evaluation of metal diapir breakup and equilibration in terrestrial magma oceans abstract due to mechanisms such as impact heating early atmospheric thermal blanketing and radioactive heating the presence of at least one global magma ocean stage in the early histories of terrestrial planets seems unavoidable in such a context a key question to constrain the early thermo chemical evolution of the earth is how much iron diapirs provided by differentiated impactors emulsified during their sinking towards the bottom of an early magma ocean in the past years several workers have focused on this question using however various approaches and making different assumptions while most studies favor rapid breakup and equilibration of iron bodies during their sinking through the magma ocean recent work suggests that iron bodies of size comparable or greater than a few tens of kilometers may preserve most of their initial volume as they reach the bottom of a magma ocean therefore leading to metal silicate disequilibrium to clarify the discrepancies and the differences among studies i have conducted a series of numerical simulations and theoretical calculations to derive the conditions and the timing for the breakup of metal diapirs of any size sinking through a silicate magma ocean with a large range of plausible viscosity values the obtained breakup criterion is used to derive stable diapir sizes and their ability to equilibrate with the surrounding silicates i show that for plausible magma ocean viscosities diapirs with initial radii smaller than the thickness of a magma ocean rapidly break up into stable diapir sizes smaller than 0 2 m at which metal silicate equilibration is rapidly achieved