carbonate platform evolution from a bioconstructed platform margin to a sand shoal system devonian guilin south china the depositional organization and architecture of the middle late devonian yangdi rimmed carbonate platform margin in the guilin area of south china were related to oblique extensional faulting in a strike slip setting the platform margin shows two main stages of construction in the late givetian to frasnian with a bioconstructed margin evolving into a sand shoal system in the late givetian the platform margin was rimmed with microbial buildups composed mainly of cyanobacterial colonies mostly renalcis and epiphyton these grew upwards and produced an aggradational locally slightly retrogradational architecture with steep foreslope clinoforms three depositional sequences s3 s5 are recognized in the upper givetian strata which are dominated by extensive microbialites metre scale depositional cyclicity occurs in most facies associations except in the platform margin buildups and upper foreslope facies in the latest givetian at the top of sequence s5 relative platform uplift subaerial exposure and associated rapid basin subsidence probably a block tilting effect caused large scale platform collapse and slope erosion to give local scalloped embayments along the platform margin and the synchronous demise of microbial buildups subsequently sand shoals and banks composed of ooids and peloids and a little later stromatoporoid buildups on the palaeohighs developed along the platform margin from which abundant loose sediment was transported downslope to form gravity flow deposits another strong tectonic episode caused further platform collapse in the early frasnian at the top of sequence s6 leading to large scale breccia release and the death of the stromatoporoid buildups siliceous facies banded cherts and siliceous shales were then deposited extensively in the basin centre as a result of the influx of hydrothermal fluids the platform margin sand shoal bank system possibly with gullies on the slope persisted into the latest frasnian until the restoration of microbial buildups four sequences s6 s9 characterized by abundant sand shoal deposits on the margin and gravity flow and hemipelagic deposits on the slope are distinguished in the frasnian strata smaller scale depositional cyclicity is evident in all facies associations across the platform slope basin transect the distinctive depositional architecture and evolution of this yangdi platform are interpreted as having been controlled mainly by regional tectonics with contributions from eustasy environmental factors oceanographic setting biotic and sedimentary fabrics

orbital scale glacio eustasy in the middle devonian detected using oxygen isotopes of conodont apatite implications for long term greenhouse icehouse climatic transitions abstract results from previous paleoclimate studies indicate gondwanan glaciation marking the onset of middle paleozoic icehouse climate conditions began by the latest devonian famennian more recently 18o trends from conodont apatite suggest cooling middle devonian subtropical seasurface temperatures 20 my prior to famennian glaciation and high latitude temperatures cool enough to permit the growth of continental glaciers which controlled longer term my scale glacio eustasy this study evaluates the details and patterns of middle devonian high frequency thirteen complete middle devonian givetian subtidal cycles 0 5 3 m thick in the little cedar formation of southeastern iowa are characterized by oxygenated offshore facies transgression poorly oxygenated offshore facies maximum flooding a return to oxygenated facies and are capped by bioturbated lower shoreface facies regression lowstand which lack evidence of subaerial exposure across shelf cyclostratigraphic facies relationships suggest relatively subdued water depth changes were responsible for cycle development measured 18o values from conodont apatite range from 15 9 to 18 4 and repeated systematic intracycle trends are dominated by lower isotopic values in offshore facies and higher isotopic values in cycle capping lower shoreface facies which is consistent with glacio eustasy driving the water depth changes the average 0 6 magnitude of intracycle isotopic shift 0 2 to 1 0 total range suggests 15 23 m glacio eustatic oscillations were responsible for observed water depth changes the higher range of intracycle isotopic magnitudes may be the result of increased subtropical evaporation rates during glacial stages which locally enriched surface seawater 18o values orbital scale

carbonate platform development in a paleoproterozoic extensional basin vempalle formation cuddapah basin india abstract sedimentological investigation of the late paleoproterozoic orosirian vempalle formation of the cuddapah basin dharwar craton india reveals three facies association that range from supratidal to deep subtidal sedimentary rocks of this succession are dominated by heterolithic carbonate mudstone intraformational carbonate conglomerate and a variety of columnar domal and stratiform microbialite facies deposition occurred in an extensional regime during development of a low gradient ramp where the distribution of microbialite facies is distinctly depth partitioned a gradual increase in synoptic relief of columnar stromatolites through the section and the upward transition from stratiform to columnar microbialites record a prolonged marine transgression with little or no influx of terrigenous detritus siliciclastic influx along the northeastern side of the shelf reflects the redistribution of topographic highs concomitant with large scale volcanic activity redistribution of topographic highs eventually led to progradation of peritidal facies and shutting down of the carbonate factory earthquake induced ground shaking and voluminous volcanism experienced by this platform point to the reactivation of a deep seated mantle plume that resulted in thermal doming of the dharwar crust prior to the onset of cuddapah deposition isotopic and elemental chemistry of a selection of vempalle formation carbonate rocks record elevated mn2 and fe2 concentrations and depleted carbon isotope values in inner ramp lagoonal facies relative to more open marine stromatolitic facies patterns of isotopic and elemental variation suggest the presence of geochemically distinct water masses either within the water column or within substrate pore fluids that resulted from a combination of globally low marine oxygenation and restricted oceanographic circulation in inner ramp environments these data suggest that even in the aftermath of early paleoproterozoic oxygenation that ocean chemistry was heterogeneous and strongly affected by local basin conditions

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

palaeomagnetic field intensity variations suggest mesoproterozoic inner core nucleation the earth s inner core grows by the freezing of liquid iron at its surface the point in history at which this process initiated marks a step change in the thermal evolution of the planet recent computational and experimental studies have presented radically differing estimates of the thermal conductivity of the earth s core resulting in estimates of the timing of inner core nucleation ranging from less than half a billion to nearly two billion years ago recent inner core nucleation high thermal conductivity requires high outer core temperatures in the early earth that complicate models of thermal evolution the nucleation of the core leads to a different convective regime and potentially different magnetic field structures that produce an observable signal in the palaeomagnetic record and allow the date of inner core nucleation to be estimated directly previous studies searching for this signature have been hampered by the paucity of palaeomagnetic intensity measurements by the lack of an effective means of assessing their reliability and by shorter timescale geomagnetic variations here we examine results from an expanded precambrian database of palaeomagnetic intensity measurements selected using a new set of reliability criteria our analysis provides intensity based support for the dominant dipolarity of the time averaged precambrian field a crucial requirement for palaeomagnetic reconstructions of continents we also present firm evidence for the existence of very long term variations in geomagnetic strength the most prominent and robust transition in the record is an increase in both average field strength and variability that is observed to occur between a billion and 1 5 billion years ago this observation is most readily explained by the nucleation of the inner core occurring during this interval the timing would tend to favour a modest value of core thermal conductivity and supports a simple thermal evolution model for the earth

non adiabaticity in mantle convection seismic observations indicate that earth s lower mantle is homogeneous as revealed by smooth depth variations of the bulk sound velocity and bullen s inhomogeneity parameter being close to one here we show with 3d spherical convection simulations that it should also be non adiabatic because a significant proportion of mantle heat sources is internal the computer simulations predict non adiabaticity of 100 300 degrees for the lower mantle geotherm with 1 01 implying that the temperature drop across the core mantle boundary exceeds 1000 degrees

solidus and liquidus profiles of chondritic mantle implication for melting of the earth across its history abstract we investigated the melting properties of a synthetic chondritic primitive mantle up to core mantle boundary cmb pressures using laser heated diamond anvil cell melting criteria are essentially based on the use of x rays provided by synchrotron radiation we report a solidus melting curve lower than previously determined using optical methods the liquidus curve is found between 300 and 600 k higher than the solidus over the entire lower mantle at cmb pressures 135 gpa the chondritic mantle solidus and liquidus reach 4150 150 k and 4725 150 k respectively we discuss that the lower mantle is unlikely to melt in the d layer except if the highest estimate of the temperature profile at the base of the mantle which is associated with a very hot core is confirmed therefore recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra low velocity zones indicate either 1 a outer core exceeding 4150 k at the cmb or 2 the presence of chemical heterogeneities with high concentration of fusible elements our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion not only complete melting of the lower mantle would require excessively high temperatures but also below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought in addition magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 gpa as suggested by siderophile metal silicate partitioning data such high surface temperature regime where thermal blanketing is inefficient points out to a transient character of the magma ocean with a very fast cooling rate

on the interaction of the geotherm with a post perovskite phase transition in the deep mantle the energy balance in the presence of a perovskite pv to post perovskite ppv transition within earth s d layer is examined in order to explore the relationship between changes in seismic velocity associated with this phase change the extent of the two phase pv ppv coexistence region and the thermal structure of the deep mantle this is motivated in part by the fact that discontinuities attributed to the pv ppv transition are inferred to be seismically sharper than permitted by some recent estimates of the pressure increment across the two phase co existence region here it is shown that sharp gradients in phase abundance may arise even when the two phase loop is very broad and therefore the pressure increment determined from thermodynamic stability alone is a poor proxy for predicting the sharpness of pv ppv related seismic discontinuities the change in ppv fraction over the steepest gradients in phase can also be highly variable which would lead to potentially complex variations in the total strength of seismic discontinuities latent heat plays an important role in the structure of the ppv phase change and its influence upon the geotherm for the double crossing scenario in which a deeper reverse transformation from ppv to pv occurs in a steep thermal boundary layer latent heat release from the shallower pv ppv transition moderates the effects of latent heat absorption at the deeper reverse transition

a long lived lunar dynamo driven by continuous mechanical stirring lunar rocks contain a record of an ancient magnetic field that seems to have persisted for more than 400 million years and which has been attributed to a lunar dynamo models of conventional dynamos driven by thermal or compositional convection have had difficulty reproducing the existence and apparently long duration of the lunar dynamo here we investigate an alternative mechanism of dynamo generation continuous mechanical stirring arising from the differential motion due to earth driven precession of the lunar spin axis between the solid silicate mantle and the liquid core beneath we show that the fluid motions and the power required to drive a dynamo operating continuously for more than one billion years and generating a magnetic field that had an intensity of more than one microtesla 4 2 billion years ago3 are readily obtained by mechanical stirring the magnetic field is predicted to decrease with time and to shut off naturally when the moon recedes far enough from earth that the dissipated power is insufficient to drive a dynamo in our nominal model this occurred at about 48 earth radii 2 7 billion years ago thus lunar palaeomagnetic measurements may be able to constrain the poorly known early orbital evolution of the moon this mechanism may also be applicable to dynamos in other bodies such as large asteroids

a hadean to paleoarchean geodynamo recorded by single zircon crystals knowing when the geodynamo started is important for understanding the evolution of the core the atmosphere and life on earth we report full vector paleointensity measurements of archean to hadean zircons bearing magnetic inclusions from the jack hills conglomerate western australia to reconstruct the early geodynamo history data from zircons between 3 3 billion and 4 2 billion years old record magnetic fields varying between 1 0 and 0 12 times recent equatorial field strengths a hadean geomagnetic field requires a core mantle heat flow exceeding the adiabatic value and is suggestive of plate tectonics and or advective magmatic heat transport the existence of a terrestrial magnetic field before the late heavy bombardment is supported by terrestrial nitrogen isotopic evidence and implies that early atmospheric evolution on both earth and mars was regulated by dynamo behavior

influence of initial cmb temperature and other parameters on the thermal evolution of earth s core resulting from thermochemical spherical mantle convection 1 here we present a wide ranging parameter study of the effects of initial core mantle boundary cmb temperature concentration of radioactive potassium in the core and density difference between harzburgite and mid ocean ridge basalt morb in a coupled spherical model of thermochemical mantle convection and parameterized core heat balance the initial cmb temperature is expected to be much higher than the solidus temperature of silicates at the base of the mantle the results indicate that as with previous purely thermal convection models the final state of the system is only weakly dependent on initial cmb temperature unless the cmb becomes blanketed by a global layer of dense material fully 3 d spherical cases have a very similar core evolution to cases in a 2 d spherical annulus giving confidence in the applicability of 2 d spherical annulus geometry for modeling earth s evolution obtaining a successful thermal evolution in the sense of obtaining the correct present day inner core size and maintaining a geodynamo over geological time is helped by the accumulation of piles of dense material at the cmb subducted morb in the present calculations and a concentration of radiogenic k in the core in the range 400 800 ppm the present day cmb heat flow is predicted to be around 9 tw while this is lower than estimates based on calculating temperature gradients in regions where the postperovskite transition is seismically imaged these tend to be areas of higher than average heat flux and thus likely overestimate the global heat flow

experimental evidence for perovskite and post perovskite coexistence throughout the whole d region article i nfo since the phase diagram for fe al bearing mgsio3 compositions at the p t conditions of the core mantle boundary remains ambiguous we investigated the fe distribution among the silicate perovskite pv and post perovskite ppv polymorphs using tandem synchrotron analyses of x ray diffraction and x ray absorption spectroscopy we performed measurements at the fe k edge of the partitioning of iron between pv and ppv up to more than 150 gpa after annealing at about 3300 k we obtain a unique solution for kfe pv ppv of 4 2 0 5 our results evidence that the two silicates should coexist over the whole d region with the main post perovskite phase being largely depleted in fe compared to the perovskite as fe and al have a dominant effect on the phase diagram these new results challenge recent determinations of the temperature profile in the lowermost mantle based on the clapeyron slope of the pv to ppv transition for pure mgsio3 composition also it appears clear that variations in the molar fractions of perovskite and post perovskite phases should be expected radially or laterally in the d region in relation with thermal or compositional heterogeneities this can help explaining the seismological anomalies observed for this mantle region finally we predict a significant increase of the feo activity in the d region which should greatly affect the chemical exchange between mantle and core

coupled core mantle thermal evolution of early mars 1 several arguments point out that at the end of planetary accretion the core of mars was likely to be much hotter than its mantle resulting in the formation of a completely or partially molten thermal boundary layer at the base of the mantle here we address the following questions how did the superheated core cool and what role did it play in the early mantle dynamics of mars we divide the coupled core mantle evolution of early mars into two stages during the first stage vigorous convection within the molten boundary layer removes the heat from the core so that the boundary layer expands up as the boundary layer gets thicker the temperature of the layer decreases eventually the temperature of the molten boundary layer drops down to the temperature for the rheological transition melt fraction 40 within 100 years this stage is described by a parameterized convection approach the second stage is modeled in spherical shell geometry using the fully three dimensional finite element code citcoms a single plume superplume forms by the instability of the thermal boundary layer the superplume stage lasts much longer on the scale of millions to hundreds of millions of years depending on the mantle viscosity during both stages of evolution the heat flux can easily satisfy the requirements for the dynamo

depositional environments and cyclicity of the early ordovician carbonate ramp in the western tarim basin nw china abstract during the early ordovician the tarim basin nw china was mainly occupied by an extensive shallow water carbonate platform on which a carbonate ramp system was developed in the bachu keping area of the western part of the basin three well exposed typical outcrop sections of the lower ordovician penglaiba formation were investigated in order to identify the depositional facies and to clarify origins of meter scale cycles and depositional sequences thereby the platform evolution thirteen lithofacies are identified and further grouped into three depositional facies associations peritidal restricted and open marine subtidal facies these lithofacies are vertically stacked into meter scale shallowing upward peritidal and subtidal cycles the peritidal cycles are mainly distributed in the lower and uppermost parts of the penglaiba formation deposited in the inner middle ramp and commonly start with shallow subtidal to intertidal facies followed by inter to supratidal facies in contrast the subtidal cycles occur throughout the formation mostly in the middle outer ramp and are dominated by shallow to relatively deep i e intermediate subtidal facies the dominance of asymmetrical and incomplete cycles suggests a dominant control of earth s orbital forcing on the cyclic deposition on the platform on the basis of vertical facies and cycle stacking patterns and accommodation changes illustrated by the fischer plots from all studied sections five third order depositional sequences are recognized in the penglaiba formation individual sequences comprise a lower transgressive part and an upper regressive one in shallow water depositional environments the transgressive packages are dominated by thicker than average subtidal cycles indicating an increase in accommodation space whereas regressive parts are mainly represented by thinner than average peritidal and subtidal cycles denoting a decrease in accommodation space in contrast in intermediate to deep subtidal environments transgressive and regressive packages display an opposite trend in accommodation space changes sequence boundaries except the basal and top boundaries of the penglaiba formation are usually represented by laterally traceable transitional boundary zones without apparent subaerial exposure features good correlation of the long term changes in accommodation space or sea level inferred from vertical stacking patterns of facies and cycles suggests an overriding eustatic control on the formation of meter scale cycles and third order depositional sequences as well as platform evolution superimposed with local and or regional tectonic influence during the early ordovician this study would help understand the controls on the tempo spatial facies distribution stratal cyclicity and carbonate platform evolution in the western tarim basin during the early ordovician facilitating prediction for favorable subsurface carbonate reservoirs and future hydrocarbon exploration and production in the penglaiba formation

core rotational dynamics and geological events a study of earth9s fluid core oscillations induced by lunar solar tidal forces together with tidal secular deceleration of earth9s axial rotation shows that the rotational eigenfrequency of the fluid core and some solar tidal waves were in resonance around 3 0 109 1 8 109 and 3 108 years ago the associated viscomagnetic frictional power at the core boundaries may be converted into heat and would destabilize the d thermal layer leading to the generation of deep mantle plumes and would also increase the temperature at the fluid core boundaries perturbing the core dynamo process such phenomena could account for large scale episodes of continental crust formation the generation of flood basalts and abrupt changes in geomagnetic reversal frequency

melting of subducted basalt at the core mantle boundary the geological materials in earth9s lowermost mantle control the characteristics and interpretation of seismic ultra low velocity zones at the base of the core mantle boundary partial melting of the bulk lower mantle is often advocated as the cause but this does not explain the nonubiquitous character of these regional seismic features we explored the melting properties of mid oceanic ridge basalt morb which can reach the lowermost mantle after subduction of oceanic crust at a pressure representative of the core mantle boundary 135 gigapascals the onset of melting occurs at 3800 kelvin which is 350 kelvin below the mantle solidus the sio2 rich liquid generated either remains trapped in the morb material or solidifies after reacting with the surrounding mgo rich mantle remixing subducted morb with the lowermost mantle

case study a 3d resistivity and induced polarization imaging from downstream a waste disposal site in brazil a contaminated site from a downstream municipal solid waste disposal site in brazil was investigated by using a 3d resistivity and induced polarization ip imaging technique this investigation purpose was to detect and delineate contamination plume produced by wastes the area was selected based on previous geophysical investigations and chemical analyses carried out in the site indicating the presence of a contamination plume in the area resistivity model has successfully imaged waste presence 31 mv v water table depth and groundwater flow direction a higher chargeability zone m 31 mv v outside wastes placement and following conductive anomaly was interpreted as a contamination plume normalized chargeability mn m confirmed polarizable zone which could be an effect of a salinity increase contamination plume and the clay presence in the environment

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

a dynamo model with double diffusive convection for mercury s core abstract a recent dynamo model for mercury assumes that the upper part of the planet s fluid core is thermally stably stratified because the temperature gradient at the core mantle boundary is subadiabatic vigorous convection driven by a superadiabatic temperature gradient at the boundary of a growing solid inner core and by the associated release of light constituents takes place in a deep sub layer and powers a dynamo these models have been successful at explaining the observed weak global magnetic field at mercury s surface they have been based on the concept of codensity which combines thermal and compositional sources of buoyancy into a single variable by assuming the same diffusivity for both components actual diffusivities in planetary cores differ by a large factor to overcome the limitation of the codensity model we solve two separate transport equations with different diffusivities in a double diffusive dynamo model for mercury when temperature and composition contribute comparable amounts to the buoyancy force we find significant differences to the codensity model in the double diffusive case convection penetrates the upper layer with a net stable density stratification in the form of finger convection compared to the codensity model this enhances the poloidal magnetic field in the nominally stable layer and outside the core where it becomes too strong compared to observation intense azimuthal flow in the stable layer generates a strong axisymmetric toroidal field we find in double diffusive models a surface magnetic field of the observed strength when compositional buoyancy plays an inferior role for driving the dynamo which is the case when the sulphur concentration in mercury s core is only a fraction of a percent

cretaceous extinctions multiple causes figure 1 deccan plateau basalts lava from deccan volcanism formed distinct layering credit gsfc nasa in the review the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary p schulte et al 5 march p 1214 2 the terminal cretaceous

the earth s core composition from high pressure density measurements of liquid iron alloys abstract high pressure high temperature in situ x ray diffraction has been measured in liquid iron alloys fe 5 wt ni 12 wt s and fe 5 wt ni 15 wt si up to 94 gpa and 3200 k in laser heated diamond anvil cells from the analysis of the x ray diffuse scattering signal of the metallic liquids we determined density and bulk modulus of the two liquid alloys comparison with a reference earth model indicates that a core composition containing 6 of sulfur and 2 of silicon by weight would best match the geophysical data models with 2 5 of sulfur and 4 5 of silicon are still consistent with geophysical constraints whereas silicon only compositions are not these results suggest only moderate depletion of sulfur in the bulk earth

cosmochemical constraints on the sulfur content in the earth s core abstract the density of the earth s core 32 5 of the mass of the earth is about 8 less than that of pure metallic fe under similar p t conditions requiring the presence of a substantial amount of a light element or light elements in the core mcqueen and marsh 1960 mcqueen and marsh 1966 sulfur is a good candidate for reducing the density on the basis of shock wave experiments ahrens 1979 estimated that 9 12 s in the core would be sufficient to account for the observed density difference this corresponds to a s content of 2 9 3 9 for the bulk earth here we present an estimate of the bulk earth s content which is based on the volatility of s in the solar nebula and the general depletion of volatile elements in meteorites and in the earth it is suggested that the ci normalized s abundance of the bulk earth is similar to or even lower than the ci normalized abundance of zn an element of similar volatility as s in the reducing environment of the solar nebula since the zn content of the mantle of the earth is well known and since the core is most likely free of zn the bulk earth s content can be calculated from the zn abundance of the mantle a maximum bulk earth s content of 0 56 and a corresponding maximum s content of the core of 1 7 are estimated the s content of the mantle is so low that the contribution to the bulk earth s content is negligible the upper limit of s in the core as derived from cosmochemical constraints is much too low to produce the required decrease in the core s density at least one other light element is needed

stacking pattern of cyclic carbonate platform strata lower cretaceous of southern apennines italy detailed sedimentological analysis of aptian albian shallow water carbonate platform strata from monte faito southern italy reveal composite sea level change the organization of the lithofacies and their related diagenetic overprint have allowed the identification of 50 elementary cycles they often show exposure related diagenetic features superimposed on subtidal deposits suggesting drops of relative sea level elementary cycles are grouped into 16 bundles forming six superbundles the hierarchical organization of the cycles are interpreted to be related to composite eustatic sea level fluctuations driven by the earth s orbital perturbation in the milankovitch frequency band moreover the systematic variation of superbundle thickness and the general evolution of the lithofacies reflects variations of accommodation potential defining longer term environmental changes different lithofacies forming elementary cycles are frequently separated by bedding planes that when viewed in a sequence stratigraphic context are interpreted as transgressive surfaces maximum flooding surfaces or sequence boundaries this allows the recognition of lowstand transgressive and highstand deposits in the cyclic units considering both the bundle superbundle ratio and the sequence stratigraphic interpretation of the superbundles a chronostratigraphic diagram illustrating both gaps at bundle level and their expected location along the section was created it establishes that the section developed over about 2 4 ma

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

first principles calculations of the lattice thermal conductivity of the lower mantle abstract the temperature variations on top of the core mantle boundary are governed by the thermal conductivity of the minerals that comprise the overlying mantle estimates of the thermal conductivity of the most abundant phase mgsio3 perovskite at core mantle boundary conditions vary by a factor of ten we performed ab initio simulations to determine the lattice thermal conductivity of mgsio3 perovskite finding a value of 6 8 0 9 w m 1 k 1 at core mantle boundary conditions 136 gpa and 4000 k consistent with geophysical constraints for the thermal state at the base of the mantle thermal conductivity depends strongly on pressure explaining the dynamical stability of super plumes the dependence on temperature and composition is weak in the deep mantle our results exhibit saturation as the phonon mean free path approaches the interatomic spacing combining our results with seismic tomography we find large lateral variations in the heat flux from the core that have important implications for core dynamics

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

lattice thermal conductivity of mgsio3 perovskite and post perovskite at the core mantle boundary abstract thermal conductivity is essential for controlling the rate of core heat loss and long term thermal evolution of the earth but it has been poorly constrained at the high pressures of earth s lowermost mantle we measured the lattice component of thermal diffusivity heat transport by scattering of phonons of both mgsio 3 perovskite pv and post perovskite ppv at high pressures of up to 144 gpa and at room temperature lattice thermal conductivity of pv dominant lowermost mantle assemblage obtained in this study is about 11 w m k while ppv bearing rocks exhibit 60 higher conductivity since such pv value is comparable to the conventionally assumed lowermost mantle conductivity our findings do not significantly alter but support the recent notion of high core mantle boundary heat flow along with a young inner core and high temperatures in the early deep earth

secular changes in tonalite trondhjemite granodiorite composition as markers of the progressive cooling of earth archean tonalite trondhjemite granodiorite associations ttg are classically thought to generate through partial melting of hydrous metabasalts however the chemical composition of the least differentiated ttg parental magmas evolved from 4 0 to 2 5 ga during this interval the mg as well as the ni and cr contents increased which is interpreted as reflecting increased interactions between felsic melts generated by metabasalt melting and mantle peridotite similarly cao na2o and sr also increased over time thus reflecting an increase in the abundance of plagioclase in the melt residue the presence or absence of residual plagioclase is interpreted in terms of melting depth the demonstrated interaction between ttg parental magmas and the mantle rules out their genesis by fusion of previously underplated metabasalt and favors the melting of subducted slab material at 4 0 ga earth s geothermal gradient was sufficiently high to allow slab melting at shallow depths where plagioclase was stable consequently due to the small thickness of the overlying mantle wedge felsic magmas interacted little with the mantle at 2 5 ga however owing to lower geothermal gradients the melting depth was greater and plagioclase became no longer stable in the thick mantle wedge overlying the subducted slab as a result felsic magmas reacted strongly with the mantle peridotite the changes of ttg composition during archean time can be thus interpreted as reflecting the progressive cooling of earth

lower triassic storm dominated ramp sequence in northern hungary an example of evolution from homoclinal through distally steepened ramp to middle triassic flat topped platform

estimates of heat flow in the deep mantle based on the power requirements for the geodynamo 1 regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle if the heat flow is too low thermal convection is shut off and the rate of generation of compositional buoyancy by the solidification of the core becomes too low to sustain the geodynamo conversely a large heat flow causes rapid growth of the inner core so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone the attendant requirements on primordial heat become more severe as the age of the inner core decreases we show that estimates of the present day heat flow satisfy the power requirements for the geodynamo however the resulting thermal history is incompatible with estimates of mantle temperatures prior to 3 ga this discrepancy can be resolved by accumulating radioactive isotopes in d or adding heat sources to the core

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

millennial scale paleoclimate cycles recorded in widespread palaeozoic deeper water rhythmites of north america rhythmically interbedded limestone and shale or limestone and chert rhythmites are a common feature of many deep water phanerozoic carbonate marine deposits seventeen different palaeozoic rhythmite successions from across north america 8 studied in detail 9 studied in reconnaissance are described and summarized individual rhythmite couplets 4 20 cm thick are composed of fine grained laminated to massive detrital limestone alternating with shale or marl or laminated spiculitic chert stratigraphic and primary depositional features within rhythmites and associated facies indicates that the carbonate rich and carbonate poor interbedding is the result of repetitive changes in sediment input primary rather than due to diagenetic redistribution of calcareous material secondary the average duration of individual rhythmite couplets is calculated using spectral analysis to determine couplet thickness combined with biostratigraphically calibrated undecompacted average sediment accumulation rates the duration of rhythmite couplets from the eight well studied successions ranges between 150 and 4900 yrs with the majority lying between 1000 and 3000 yrs i e millennial scale the paucity and low diversity of skeletal and trace fossils preserved suspension laminae lack of sediment reworking and facies associations indicate rhythmite accumulation was favored by 1 deposition below storm wave base which limited reworking by currents 2 dysaerobic bottom waters which restricted bioturbation and intermixing of interbedded lithologies and 3 proximity to nearshore carbonates supplying abundant fine grained detrital carbonate these combined conditions were best met along flooded subtropical continental shelves or epeiric seas during my scale 3rd order sealevel rises the rhythmic alternation between carbonate rich and carbonate poor layers is interpreted to represent millennial scale paleoclimatic changes related to 1 wet dry climate cycles which influenced the amount of continent derived eolian and or fluvial sediment input 2 variations in offshore transport via storm generated or density currents of nearshore derived terrigenous or carbonate sediments and or 3 changes in wind driven upwelling and availability of recycled biogenic silica the various rhythmite successions accumulated under dramatically different paleoenvironment and paleogeographic conditions including active to passive tectonic settings equatorial to subtropical latitudes long term icehouse through greenhouse climatic conditions calcite versus aragonitic seas variable atmospheric co2 concentrations before and after land plant and animal evolution and across widely varying ocean basin configurations if our short term paleoclimatic interpretations for the rhythmites are correct then it is apparent that millennial scale climate changes occurred over a very wide spectrum of paleoceanographic paleogeographic paleoclimatic tectonic and biologic conditions and over time periods from the cambrian to the quaternary given this it is difficult to invoke models of internally driven thermohaline oceanic oscillations or continental ice sheet instabilities to explain their origin instead we suggest that

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

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

carbon isotope lateral variability in a middle frasnian carbonate platform belgium significance of facies diagenesis and sea level history abstract carbon isotopic variations of frasnian shallow water carbonates from belgium are related to facies and major sea level trends the influence of the diagenetic overprint was assessed in order to determine the primary signal of the frasnian carbonates shallow water microfacies are characterized by biostromes with stromatoporoids and lagoonal deposits dominated by carbonate mud and calcareous algae with subaerial exposure surfaces the diagenetic history was controlled by three main events early meteoric diagenesis short term subaerial exposure during deposition late meteoric diagenesis major famennian regression and burial diagenesis the oxygen isotopic values are almost constant with respect to facies original material carbonate mud and cement and sedimentological units no differences before or after the main regression this homogeneity is related to resetting during late meteoric diagenesis the carbon isotopic values are related to facies with the more negative values for the shallowest facies and to major sea level variations most negative values after the main regression this pattern is interpreted as being related to primary signals this trend was enhanced by early meteoric diagenesis and the influence of more negative values from paleosols the carbon isotope patterns reflect the influence of sea level and water circulation on shallow water deposits and this influence implies that shallow water carbonates are not necessarily good material for assessing the primary isotopic values of the ocean because of the influence of long residence time aging of the platform top water and because of early diagenesis

constraints from material properties on the dynamics and evolution of earth s core the material properties of the earth s core have been better constrained by recent technical and computational advances the properties imply that the core was once hot but is cooling quickly and the inner core is young

coeval versus reciprocal mixed carbonate siliciclastic deposition middle devonian baltic basin eastern europe implications from the regional tectonic development the middle devonian narva succession in the baltic basin represents a significant turnaround in the history of the basin the detailed study of core and outcrop sections and the three dimensional correlations across the baltic basin reveal a carbonate dominated mixed retrogressive succession overlain by a siliciclastic dominated progradational succession the palaeogeographic reconstructions show how the shallow tide influenced basin expanded from south west to north east and later during the transgression also to the north south and east the transgressive portion of the basin fill is dominated by carbonate rich sabkha and supratidal to intertidal deposits on the basin margins and subtidal carbonates in the basin centre siliciclastic material was derived by tidal currents and storm waves from the south west through a tidal inlet and flood tidal delta complex this initial transgressive phase is characterized by the lack of subsidence or even episodic uplifts in the northern north western part of the basin margin shown by convergence of timelines and the thin 30 m transgressive succession in contrast on the southern margin the facies associations stack vertically into a 70 to 80 m thick succession indicating significantly higher subsidence rates the upper part of the transgressive phase indicates subsidence across the whole basin the upper progradational portion of the basin fill is dominated by coarse siliciclastic tide influenced deltaic deposits that rapidly prograded from north west to south east this detailed study on the narva succession shows that siliciclastic and carbonate deposition was coeval and that mixing occurred at different temporal and spatial scales the mixing was controlled by grain size volume and location of siliciclastic input rather than relative sea level changes as suggested in widely used reciprocal mixing models it is suggested that the forebulge of the scandinavian caledonian fold and thrust belt migrated to the north western margin of the baltic basin during the earliest eifelian as indicated by the lack of subsidence and probable uplift in the northern north western margin during the early transgressive phase the forebulge migration ceased although the forebulge had already started to subside during the later stages of the transgressive phase the deltaic progradation is interpreted to be associated with the orogenic collapse and uplift in the scandinavian caledonides that caused the erosion of the foreland basin fill and the coarse sediment transport into the baltic basin

mantle regulation of core cooling a geodynamo without core radioactivity abstract the case for radioactivity in the core based on the power requirements of the geodynamo is re evaluated previous calculations of mantle regulation of core thermal evolution have used an inappropriate formula new calculations with a more appropriate formula yield lower core heat loss in the past thus mitigating the implication of unreasonably high past core and mantle temperatures multiple thermal evolutions leading to present heat flows are also demonstrated depending on the efficiency of mantle removal of core heat some with moderately high past core heat loss and some with low and steady core heat loss the latter would permit a low or moderate power dynamo without core radioactivity key uncertainties are the efficiency of core cooling by the mantle the thermal conductivity of the core and the energy or entropy flow required to maintain the dynamo the present rate of heat loss from the core is argued to be still rather uncertain and a commonly used estimate of the thermal conductivity of the core is shown plausibly to be too high and in any case to be uncertain by perhaps a factor of 2 the geochemical difficulties associated with postulating radioactive heat sources in the core are stressed

stratigraphic completeness of carbonate dominated records from continental interiors versus continental margins stratigraphic thinning occurs via condensation and omission at multiple scales abstract over phanerozoic time scales stratigraphic records from continental interiors or cratons are dramatically thinner and are generally assumed to be relatively incomplete with more numerous and longer duration hiatuses compared to records from more rapidly subsiding continental margins however this assumption need not be true for the shorter time scales i e several 106 years and shorter over which accumulation of the preserved stratigraphic record on the continental interior actually takes place this study compares carbonate dominated sedimentary records from the devonian continental interior iowa and continental margin nevada to evaluate whether the continental interior record is 1 miniaturized i e thinner but equally complete 2 comparable in thickness and quality where the sedimentary record is preserved but certain portions of the record are notably absent i e omitted or truncated or 3 so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental margin record this study finds that fourth to fifth order cycles in iowa are on average approximately half as thick and half as numerous compared to the continental margin of nevada moreover the stratigraphic record on the continental margin of nevada is dominated by cycles that are composed of tidal flat and shallow subtidal lithofacies capped by simple flooding surfaces and exhibit catch up or keep up depositional styles the continental interior record in iowa is dominated by cycles that are composed of subtidal lithofacies capped by a range of bounding surfaces and exhibit catch down or give up depositional styles these findings suggest that the thin record in iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric sea setting rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record

an alternative methodology for the analysis of electrical resistivity data from a soil gas study the aim of this paper is to present an alternative method for the analysis of resistivity data the methodology was developed during a study to evaluate if electrical resistivity can be used as a tool for analysing subsurface gas dynamics and gas emissions from landfills the main assumption of this study was that variations in time of resistivity data correspond to variations in the relative amount of gas and water in the soil pores field measurements of electrical resistivity static chamber gas flux and weather data were collected at a landfill in helsingborg sweden the resistivity survey arrangement consisted of nine lines each with 21 electrodes in an investigation area of 16 x20 m the abem lund imaging system provided vertical and horizontal resistivity profiles every second hour the data were inverted in res3dinv using l 1 norm based optimization method with a standard least squares formulation each horizontal soil layer was then represented as a linear interpolated raster model different areas underneath the gas flux measurement points were defined in the resistivity model of the uppermost soil layer and the vertical extension of the zones could be followed at greater depths in deeper layer models the average resistivity values of the defined areas were calculated and plotted on a time axis to provide graphs of the variation in resistivity with time in a specific section of the ground residual variation of resistivity was calculated by subtracting the resistivity variations caused by the diurnal temperature variations from the measured resistivity data the resulting residual resistivity graphs were compared with field data of soil moisture precipitation soil temperature and methane flux the results of the study were qualitative but promising indications of relationships between electrical resistivity and variations in the relative amount of gas and water in the soil pores were found even though more research and better data quality is necessary for verification of the results presented here we conclude that this alternative methodology of working with resistivity data seems to be a valuable and flexible tool for this application

a seismic model of a partially molten inner core fearn et al 1981 recently proposed a mechanism whereby the inner core contains a significant fraction of liquid we construct a model of a partially molten inner core compatible with seismic observation specifically we develop an improved model of bulk anelasticity including the effect of thermal and material diffusion and show that it is quantitatively capable of explaining the observed anelasticity also studies of the reflection of seismic waves from the inner core boundary are used to estimate the mass fraction of liquid in the inner core

neoproterozoic chuar group 800 742 ma grand canyon a record of cyclic marine deposition during global cooling and supercontinent rifting abstract chuar group sediments were deposited in a marine cratonic basin synchronously with marine deposition in other basins of western north america and australia the top of the chuar group is 742 ma thus this succession offers a potentially important record of global climatic and tectonic changes during the mid neoproterozoic a critical time leading to possible global glaciation during supercontinent rifting chuar group cycles and sequences may record glacioeustatic fluctuations during the climatic transition into the sturtian ice age 750 700 ma as well as extension related to the dispersal of rodinia the mid neoproterozoic chuar group 1600 m thick is predominantly composed of mudrock with subordinate meter scale beds of dolomite and sandstone facies analysis leads to the interpretation of a wave and tidal influenced marine depositional system diagnostic marine features include 1 marine fossils and high local pyrite content in the mudrock facies 2 mudcracked mud draped symmetric ripples and reverse flow indicators in the sandstone facies 3 facies associations between all facies and 4 no unequivocal terrestrial deposits chuar facies stack into 320 dolomite and sandstone capped meter scale cycles 1 20 m thick and non cyclic intervals of uniform mudrock facies 20 150 m thick nearly all cycles have mudrock bases indicating subtidal water depths dolomite capped cycles shallow to peritidal environments peritidal cycles some indicating subaerial exposure of varying degrees exposure cycles sandstone capped cycles shallow to peritidal environments with no evidence of prolonged exposure peritidal cycles non cyclic intervals represent the deepest water depths 10s of meters peritidal cycles and non cyclic intervals dominate the lower and middle chuar group in the upper chuar group the percentage of exposure cycles increases as does the thickness of individual cycles and non cyclic intervals and the degree of subaerial exposure in the cycle caps correlation of cycles across 10 km shows that many cycles are laterally continuous and some vary in thickness some thickness changes are coincident with local and regional extensional structures these cycle trends reflect a resolvable mixture of tectonic and climatic controls cycles are interpreted to be high frequency and glacioeustatically controlled based on comparison of cycle character and thickness to phanerozoic examples and lateral continuity of many cycles respectively cycles in the lower and middle chuar group show characteristics suggestive of low amplitude sea level changes similar to meter scale cycles from global greenhouse climates in the phanerozoic upper chuar group cycles show characteristics suggestive of moderate amplitude sea level changes similar to phanerozoic greenhouse icehouse transition climates indicating an increase in continental ice volume variability in cycle thickness and lateral pinching of some cycle caps is controlled by variable tectonic subsidence evidenced by thickening trends coincident with active rift related structures and also by variability in sediment supply the presence of dolomite caps in this otherwise siliciclastic succession is interpreted to be due largely to rapid changes in climate related to short term glacioeustatically controlled sea level changes four crude lithostratigraphic sequences 150 775 m thick are defined based on dolomite poor to dolomite rich stratigraphic intervals long term changes in cycle cap lithology may be driven by long term changes in climate similar to short term glacioeustatic controls on meter scale cycle cap lithology large scale thickness variability in these sequences is due to local differential tectonic subsidence

regional to global correlation of lower cretaceous hauterivian barremian shallow water carbonates of the southern apennines italy and dinarides montenegro southern tethyan margin abstract we propose a high resolution regional to global scale correlation of two hauterivian barremian shallow water carbonate platform sections belonging to different palaeogeographic domains of the southern margin of the tethys these successions are now located more than 500 km apart and are represented by 137 m of core drilled at monte raggeto southern apennines italy and by 80 m of well stratified rocks cropping out in the podgorica mountains dinarides montenegro they display three superimposed orders of stratigraphic cyclicity defined by elementary cycles grouped into bundles and superbundles and attributed to orbitally induced composite sea level fluctuations elementary cycles are interpreted as the precession and the obliquity periodicities 20 40 ky while bundles and superbundles correspond to the short 100 ky and long 400 ky eccentricity cycles respectively as both the ratios between the elementary cycles and the bundles and between the bundles and the superbundles do not always reflect the classical 5 1 and 4 1 relationship the sedimentary record of both the studied sections is likely to include omission of bundles or their portion the general evolution of depositional and diagenetic facies the vertical change in thickness of the cyclic units and the interpretation of superbundles as small scale depositional sequences suggest that elementary cycles and their groups are superimposed on lower frequency environmental oscillations these display an upward transgressive regressive trend t rt of the facies and testify to larger scale variations of accommodation potential on the shelf t rts sequence stratigraphic interpretation of the superbundles as well as the common occurrence of the biostratigraphic dated hauterivian barremian boundary in the studied sections support the long distance regional correlation between the successions to be carried out on the 100 ky scale moreover by assuming the maximum flooding intervals of time equivalent superbundles as virtually isochronous intervals we have detected stratigraphic gaps of 1200 and 600 ky in the monte raggeto and in the podgorica mountains sections respectively both sections are formed of 10 complete superbundles each of them testifying to the 400 ky long eccentricity hence the monte raggeto and podgorica mountains successions represent a duration of at least 4 0 my in terms of elapsed time regardless of gaps within the stratigraphic record finally a correlation between the orbitally induced compared sections and both the 3rd order tethyan stratigraphic cycles and the global cycle chart is suggested our study confirms that cyclically organized shallow marine carbonate platform deposits controlled by orbitally induced sea level fluctuations represent a powerful tool for high precision regional and global correlations this can be of fundamental importance for quantification of sedimentary diagenetic and evolutionary processes as well as for the understanding of autocyclic versus allocyclic control on sequence development

possible heterogeneity of the earth s core deduced from pkikp travel times the core of the earth is usually described by spherically symmetrical velocity models the core is made of two main spherical layers the fluid outer core with a radius close to 3 480 km and a p velocity increasing with depth from 8 km s 1 to 10 3 km s 1 and the solid inner core with a radius of 1 220 km and a p velocity close to 11 km s 1 refs 1 2 station residuals of the seismic core phase pkikp have been computed for 400 seismological observatories worldwide using 5 yr of the international seismological centre isc bulletins pkikp travel times can be corrected for upper mantle propagation by subtracting p delays thus pkikp p residuals are a measurement of the average vertical travel times in the lower mantle and in the core of the earth beneath seismic stations a spherical harmonic development of pkikp p delays up to degree 4 explains 58 of the variance in the data pkikp p exhibit a latitudinal dependence polar stations tend to be faster than equatorial stations we show here that this pattern may reflect a departure from spherical symmetry in the p velocity distribution in the vicinity of the inner core boundary of the earth

solid liquid iron partitioning in earth s deep mantle iron in partially molten rocks under deep mantle conditions partitions into the melt phase less than previously reported suggesting that melt generated near the core mantle boundary should segregate upwards denis andrault et al investigate phase relationships in partially molten rocks under deep mantle conditions and find that iron in the rocks partitions into the melt phase to a lesser extent than has previously been reported the calculated densities of the solid and melt phases suggest that melt generated near the core mantle boundary should be buoyant and hence should segregate upwards melting processes in the deep mantle have important implications for the origin of the deep derived plumes believed to feed hotspot volcanoes such as those in hawaii1 they also provide insight into how the mantle has evolved geochemically and dynamically since the formation of earth2 melt production in the shallow mantle is quite well understood but deeper melting near the core mantle boundary remains controversial modelling the dynamic behaviour of deep partially molten mantle requires knowledge of the density contrast between solid and melt fractions although both positive and negative melt buoyancies can produce major chemical segregation between different geochemical reservoirs each type of buoyancy yields drastically different geodynamical models ascent or descent of liquids in a partially molten deep mantle should contribute to surface volcanism or production of a deep magma ocean respectively we investigated phase relations in a partially molten chondritic type material under deep mantle conditions here we show that the iron partition coefficient between aluminium bearing mg fe sio3 perovskite and liquid is between 0 45 and 0 6 so iron is not as incompatible with deep mantle minerals as has been reported previously3 calculated solid and melt density contrasts suggest that melt generated at the core mantle boundary should be buoyant and hence should segregate upwards in the framework of the magma oceans induced by large meteoritic impacts on early earth our results imply that the magma crystallization should push the liquids towards the surface and form a deep solid residue depleted in incompatible elements

earth s core and the geodynamo earth s magnetic field is generated by fluid motion in the liquid iron core details of how this occurs are now emerging from numerical simulations that achieve a self sustaining magnetic field early results predict a dominant dipole field outside the core and some models even reproduce magnetic reversals the simulations also show how different patterns of flow can produce similar external fields efforts to distinguish between the various possibilities appeal to observations of the time dependent behavior of the field important constraints will come from geological records of the magnetic field in the past

sequence stratigraphy and platform evolution of lower middle devonian carbonates eastern great basin lower middle devonian carbonates 270 400 m thick of the eastern great basin were deposited along a low energy westward thickening carbonate platform six regional facies representing peritidal shallow subtidal stromatoporoid biostrome deep subtidal slope and basin environments are recognized four third order 1 5 2 5 m y durations transgressive regressive sequences are identified across the platform to basin transition based on deepening and shallowing patterns in regional facies intensity and stratigraphic distribution of subaerial exposure features and stacking patterns of fourth to fifth order upward shallowing peritidal and subtidal cycles transgressive systems tracts along the basin slope are characterized by upward deepening successions of proximal through distal turbidites overlain by fine grained hemipelagic deposits shallow platform transgressive systems tracts are composed of stacks of thicker than average peritidal cycles overlain by subtidal cycles or noncyclic deep subtidal facies maximum flooding zones along the shallow platform are composed of stacked peritidal cycles dominated by subtidal facies noncyclic deep subtidal facies or distinct deeper subtidal units within successions of restricted shallow subtidal or peritidal facies highstand systems tracts along the basin slope are composed of hemipelagic deposits overlain by distal through proximal turbidites highstand systems tracts along the shallow platform are characterized by upward shallowing succession of cyclic peritidal through shallow subtidal facies sequence boundary zones 2 16 m thick along the shallow platform are composed of exposure capped peritidal and subtidal cycles that exhibit upsection increases in the proportion of tidal flat subfacies and increases in the intensity of cycle capping subaerial exposure features sequence boundary zones along the basin slope 6 20 m thick are composed of upward shallowing successions of proximal turbidites or by platform margin peloid shoal deposits the absence of exposure features and meter scale cycles within basin slope sequence boundary zones indicates that the combined rates of third through fifth order sea level fall rates were less than tectonic subsidence rates sequence stratigraphic correlations between contrasting facies belts of the basin slope section na and the edge of the shallow platform section tm were independently verified with high resolution conodont and brachiopod biostratigraphy correlation of sequences 1 4 with transgressive regressive sequences of similar age in the western midwestern and eastern united states western canada and europe indicates they are eustatic in origin systems tract scale correlations across the study area indicate that the platform evolved from a homoclinal ramp to a distally steepened ramp then into a flat topped platform sequences 1 2 an incipiently drowned intraplatform basin developed during sequence 3 as the result of third order sea level rise and differential sediment accumulation rates between the platform margin and intraplatform basin during deposition of highstand systems tract 3 progradation infilled the intraplatform basin resulting in a flat topped platform a distally steepened ramp developed during transgressive systems tract maximum flooding zone 4 and evolved into a flat topped platform during highstand systems tract 4 deposition the four sequences stack in an aggradational to slightly progradational pattern keep up style sedimentation and are bound by sequence boundary zones rather than unconformities suggesting that greenhouse climate modes and second order accommodation gains related to the lower portion of the second order kaskaskia sequence controlled sequence scale stacking patterns

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

episodic earth evolution abstract u pb ages of zircons from precambrian granitoids and major rivers are grouped into a series of major peaks at about 2 7 2 5 2 1 1 9 and 1 1 ga recently these peaks have been interpreted as times of enhanced preservation of the continental crust associated with the assembly of supercontinents an older interpretation which we support is that they correspond instead to periods of accelerated crustal growth related to episodic convection of the mantle in this paper we use fluid mechanics experiments to develop a new model of mantle convection and crustal growth a dense layer at the base of the mantle persists until 2 7 ga when it destabilizes and generates large domes that rise into the upper mantle there they cause a large increase in the rate of subduction which leads to enhanced granite magmatism at convergent margins and thus to a pulse of crustal growth the domes heat the upper mantle which partially melts at mid ocean ridges to produce thick oceanic crust that resists subduction the subsequent period of subdued plate motion is broken by the next generation of mantle domes before and after the archean proterozoic period of episodic crustal growth plate tectonics operated quasi continuously

upper devonian carbonate platform correlations and sea level variations recorded in magnetic susceptibility abstract this paper concerns the analysis of four outcrops in the frasnian upper devonian of belgium we compare the results of a precise sedimentological analysis with magnetic susceptibility ms data this comparison allows us to improve stratigraphic correlations and to test the relationship between magnetic susceptibility and sea level changes considering the sedimentological study different microfacies have been identified from the external belt dominated by relatively argillaceous open marine facies with crinoids to the biostromal and the lagoonal belt dominated by algae rich muddy facies fourth and third order sequences have also been identified and are probably related to sea level variations magnetic susceptibility data provides us very good fourth order correlations and the link between magnetic susceptibility and different sedimentological parameters is obvious more precisely ms appears to be related to fourth and third order sequences and to microfacies

thermal and chemical evolution of the terrestrial magma ocean abstract the earth is likely to have experienced a magma ocean stage during accretion thermal and chemical evolution of magma ocean is investigated based on a one dimensional two phase flow heat and mass transfer model differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere if the magma ocean is formed by the blanketing effect of a solar type proto atmosphere extensive differentiation proceeds at lower mantle pressure if the magma ocean is formed by the blanketing effect of an impact induced steam atmosphere no differentiation at lower mantle pressure is likely if a very deep magma ocean is formed by a giant impact whether differentiation proceeds at lower mantle pressure or not depends on grain size viscosity of melt and or properties of a transient atmosphere on the contrary chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type a shallow magma ocean can remain for 100 200 my without any heating processes

cyclostratigraphy of middle devonian carbonates of the eastern great basin abstract middle devonian carbonates 250 430 m thick of the eastern great basin were deposited along a low energy westward thickening distally steepened ramp four third order sequences can be correlated across the ramp to basin transition and are composed of meter scale upward shallowing carbonate cycles or parasequences peritidal cycles shallow subtidal facies capped by tidal flat laminites constitute 90 of all measured cycles and are present across the entire ramp the peritidal cycles are regressive and transgressive prone upward deepening followed by upward shallowing facies trends approximately 80 of the peritidal cycle caps show evidence of prolonged subaerial exposure including sediment filled dissolution cavities horizontal to vertical desiccation cracks rubble and ka st breccias and pedogenic alteration locally these features are present down to 2 m below the cycle caps subtidal cycles capped by shallow subtidal facies are present along the middle outer ramp and ramp margin and indicate incomplete shallowing submerged subtidal cycles 64 of all subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies exposed subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies that are capped by features indicative of prolonged subaerial exposure dissolution cavities and brecciation average peritidal and subtidal cycle durations are between approximately 50 and 130 k y fourth to fifth order the combined evidence of abundant exposure capped peritidal and subtidal cycles transgressive prone cycles and subtidal cycles correlative with updip peritidal cycles indicates that the cycles formed in response to fourth to fifth order glacio eustatic sea level oscillations sea level oscillations of relatively low magnitude 10 m are suggested by the abundance of peritidal cycles the lack of widely varying water depth dependent facies within individual cycles and the presence of noncyclic stratigraphic intervals within intrashelf basin slope and basin facies noncyclic intervals represent missed subtidal beats when the seafloor lay too deep to record the effects of the short term sea level oscillations exposure surfaces at the tops of peritidal and subtidal cycles represent one or more likely several missed sea level oscillations when the platform lay above fluctuating sea level but the amplitude of fourth to fifth order sea level oscillation s were not high enough to flood the ramp the large number of missed beats exposure capped cycles specifically in sequences 2 and 4 results in fischer plots that show poorly developed rising and falling limbs subdued wave like patterns consequently the fischer plots are of limited use as a correlation tool for these particular depositional sequences the abundance of missed beats also explains why milankovitch type cycle ratios 5 1 or 4 1 are not observed and why such ratios would not be expected along many peritidal cycle dominated carbonate platforms

dynamics of cyclic carbonate deposition and biotic recovery on platforms during the famennian of late devonian in guangxi south china constraints from high resolution cycle and sequence stratigraphy to better understand the dynamics of platform carbonate deposition evolution and biotic recovery during the famennian high resolution cycle and sequence stratigraphic analyses were carried out upon three platform sections one in ramp and two in rimmed platforms along with a biostratigraphically well constrained basinal section in guangxi south china four main facies and fourteen lithofacies are identified in the three isolated platforms these are vertically arranged into decimetre to metre scale shallowing upward peritidal and subtidal cycles or parasequces in which the peritidal cycles predominate over the lower middle famennian six third order sequences s1 to s6 are identified based on the cycle stacking patterns as illustrated by fischer plots and vertical facies changes these sequences are temporally calibrated through correlation with basinal sequences constrained with conodont zonation and match well the six main famennian transgressive regressive cycles t1 to t6 in euramerica and elsewhere indicating a eustatic control however an opposite longer term trend in accommodation change s3 to s4 between platform interior and deeper open shelf to basin settings during the middle famennian suggests a differential subsidence across the platform basin section likely driven by block tilting thus both eustatic fluctuations and local tectonism had played an important role in platform development and evolution after the frasnian famennian biotic crisis main marine benthos preferentially recovered in the normal marine niches on the nearshore open shelves and radiated gradually into offshore restricted platforms brachiopods notably rhychonellides were the taxa recovering the earliest s1 in the normal or near normal marine conditions then echinoderms s3 stromatoporoids upper s3 and corals s5 stepped in episodically however these benthos generally appeared later in the restricted platform interiors only as if the ecological conditions were improved well enough for their colonization therefore the biotic recovery processes were diachronous both taxonomically and ecologically specified

millennial scale climate origins for stratification in cambrian and devonian deep water rhythmites western usa abstract basinal facies of the middle cambrian marjum formation western utah and middle devonian denay limestone central nevada are characterized by thin rhythmically interbedded limestone and marl layers deep water rhythmites limestone layers average thickness range of 4 3 5 5 cm are composed of laminated to massive pelleted lime mudstone marl layers average thickness range of 0 7 1 7 cm are characterized by laminated argillaceous dolomitic mudstone the absence of current or wave reworked features paucity of bioturbation and skeletal fossils stratigraphic relationships with adjacent facies and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet dysaerobic waters below storm wave base both limestone and marl layers are composed of submillimeter thick graded laminae which represent discrete depositional events from dilute density currents generated by high frequency storms or distal turbidity currents fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the mesozoic instead the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and or eolian influx or changes in marine currents storm or distal turbidity currents which transported shallow platform derived carbonate material into the deep water region spectral analysis of carbonate time series were compared to lithologic rank series and particularly for the middle cambrian rhythmites were found to be statistically indistinguishable the durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections these rates range between 4 3 4 1 cm k y and 21 2 29 2 cm k y for the cambrian and 3 6 1 8 cm k y to 5 1 7 4 cm k y for the middle devonian application of these sedimentation rates to the marjum couplets suggests that individual couplets represent between 190 2100 years of time the denay couplets represent 800 1900 years the good agreement between empirical holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the paleozoic rhythmites supports this millennial scale interpretation these results combined with that from previous work in paleozoic evaporite and carbonate successions suggest that millennial scale paleoclimatic variations affected marine and marginal marine sedimentation as far back in time as the cambrian millennial scale climatic change appears to be a permanent feature affecting the oceans and atmosphere and is apparently largely unaffected by major changes in phanerozoic paleogeography tectonics and atmospheric composition

causes and consequences of outer core stratification abstract the earth s outer core appears to be compositionally layered exotic mechanisms such as an original chemically layered core preserved from the earth s accretionary period or compositionally different core material delivered by a moon creating impactor are conceivable but require a core whose outermost part has been stratified throughout core history relying on unknowable processes to achieve barodiffusion and core mantle reaction lead to layers significantly thinner than observed we show that a balance of mass transferred from the inner core to the top of the outer core is possible and that the stratification could arise as a byproduct of light element accumulation however if a subadiabatic thermal gradient at the top of the outer core exists that quells radial flow it could serve as a witness of light element accumulation by preventing mixing with the convecting part of the core the temperature difference through a subadiabatic layer could be 80 300 k and carry heat fluxes through the core mantle boundary of 0 5 23 tw given uncertainty in core properties

cyclostratigraphy and sequence boundaries of inner platform mixed carbonate siliciclastic successions barremian aptian zonguldak nw turkey abstract barremian aptian shallow marine mixed carbonate siliciclastic successions of the zonguldak area nw turkey have been studied in detail along three measured stratigraphic sections field and laboratory analysis of microfacies and sedimentary structures have demonstrated that sections are composed of meter scale shallowing upward cycles cyclicity of shallow water mixed carbonate siliciclastic successions are generally observed in the form of alternating sandstone siltstone or sandy limestone and limestone a prominent level of charophyte packstone within the successions of zonguldak and kozlu is interpreted as a sequence boundary in the cengellidere section cyclicity is generally represented by an alternation of sandstone conglomerate and bioclastic limestone the first level of conglomerate within the section is interpreted as a sequence boundary smaller scale cyclic arrangements are also recorded within meter scale cycles 4th 5th and 6th order cycles are superimposed and create a hierarchical stacking however 6th order cycles present a relatively random distribution and termed as episodic thickness variation of cycles along the section and frequency of sand and or silt rich cycle types are used to interpret systems tracts within the sequences

the frasnian famennian mass extinction insights from high resolution sequence stratigraphy and cyclostratigraphy in south china two sequences sfr sfa each 1 1 2 myr in duration are recognised in the strata across the frasnian famennian f f transition both in carbonate platform and interplatform basinal successions in south china the sequence boundary between the two sequences is placed a little below the top of the frasnian the sequences are basically composed of coarsening upward bed thickness increasing upward cycles and shallowing upward cycles parasequences in basinal and platform deposits respectively which stack into cycle sets typically six to eight cycles 10 and 12 cycle sets are identified in sequences sfr and sfa respectively these cycle sets can be further grouped into larger scale composite cycle sets herein termed mesocycle and megacycle sets with two and four cycle sets respectively this vertical cycle stacking pattern and the hierarchy of cyclicity suggest a milankovitch style of forcing such that the cycles and cycle sets were formed in response to the orbital perturbations of precession 16 18 kyr and eccentricity v100 kyr in duration respectively in the basinal cycles smaller scale rhythmic stratification beds typically six to eight beds in a cycle are extensive and were likely caused by millennial scale climatic forcing in the lower sequence sfr the latest highstand deposits consist of calciturbidites and debrites in deep water strata and fenestral limestones in shallow water strata representing a major third order sea level fall within these deposits four cycle sets are further identified in both coeval deep water and platform successions succeeding deeper water organic rich facies within which three cycles occur are the transgressive deposits of the overlying famennian sequence sfa these cycles represent three higher frequency 16 18 kyr sea level fluctuations and accompanying anoxia superimposed on a major third order sea level rise the f f boundary is placed at the top of the first cycle based on conodont data thus a major sea level fall and then a rise occurred in the f f transitional period faunal and sedimentological data reveal a massive biotic decline in concert with the major sea level fall and a further biotic demise coinciding with the major sea level rise and its three superimposed higher frequency sea level fluctuations and accompanying anoxia the f f biotic crisis was therefore characterised by two episodes of step down extinction on the basis of milankovitch orbital rhythms the first major biotic extinction took place over v400 kyr and the subsequent event was v50 kyr in duration i e v450 kyr for the entire event at the same time as the massive decline of normal marine fossils during the latest frasnian sea level fall there was widespread cyanobacterial growth and a thriving of planktonic calcispheres suggesting eutrophic conditions this situation could have caused a severe biotic loss as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over

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

carbonate platform growth and cyclicity at a terminal proterozoic passive margin infra krol formation and krol group lesser himalaya india the infra krol formation and overlying krol group constitute a thick 2 km carbonate rich succession of terminal proterozoic age that crops out in a series of doubly plunging synclines in the lesser himalaya of northern india the rocks include 18 carbonate and siliciclastic facies which are grouped into eight facies associations 1 deep subtidal 2 shallow subtidal 3 sand shoal 4 peritidal carbonate complex 5 lagoonal 6 peritidal siliciclastic carbonate 7 incised valley fill and 8 karstic fill the stromatolite rich peritidal complex appears to have occupied a location seaward of a broad lagoon an arrangement reminiscent of many phanerozoic and proterozoic platforms growth of this complex was accretionary to progradational in response to changes in siliciclastic influx from the south eastern side of the lagoon metre scale cycles tend to be laterally discontinuous and are interpreted as mainly autogenic variations in the number of both sets of cycles and component metre scale cycles across the platform may result from differential subsidence of the interpreted passive margin apparently non cyclic intervals with shallow water features may indicate facies migration that was limited compared with the dimensions of facies belts correlation of these facies associations in a sequence stratigraphic framework suggests that the infra krol formation and krol group represent a north to north westfacing platform with a morphology that evolved from a siliciclastic ramp to carbonate ramp to peritidal rimmed shelf and finally to open shelf this interpretation differs significantly from the published scheme of a basin centred on the lesser himalaya with virtually the entire infra krol krol succession representing sedimentation in a persistent tidal flat environment this study provides a detailed neoproterozoic depositional history of northern india from rift basin to passive margin and predicts that genetically related neoproterozoic deposits if they are present in the high himalaya are composed mainly of slope basinal facies characterized by fine grained siliciclastic and detrital carbonate rocks lithologically different from those of the lesser himalaya

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

experimental determination of the effect of h2o on the 410 km seismic discontinuity abstract due to the high solubility of h 2 o in the mineral wadsleyite it has been recognized that the presence of h 2 o in the mantle could influence the pressure and pressure interval of the olivine to wadsleyite phase transformation that is generally considered to be the cause of the 410 km seismic discontinuity we have performed multianvil experiments in the mg 2 sio 4 h 2 o system in order to quantify the expansion of the wadsleyite stability field as a result of the presence of h 2 o at 1200 c we find that the wadsleyite stability field expands to lower pressures by approximately 1 gpa under h 2 o rich fluid saturated conditions at 1400 c the expansion is approximately 0 4 gpa and no expansion can be detected at 1600 c a thermodynamic model based on recent h 2 o solubility measurements and crystallographic observations predicts an expansion of the wadsleyite stability field that is in good agreement with the experimental results when these results are combined with phase relations in the mg 2 sio 4 fe 2 sio 4 system it can be shown that significant effects on the pressure and pressure interval of the olivine to wadsleyite transformation i e on the depth and width of the 410 km discontinuity are only expected at lower than ambient mantle temperatures 2 o concentrations that are substantially greater than 0 2 wt areas of the mantle where the 410 km discontinuity appears to occur over a depth interval of over 20 km can only be explained if the temperature in these regions is at or below 1200 c and water concentrations are close to the level where olivine would become h 2 o saturated i e 0 5 wt the presence of ferric fe in the mantle however may also play a role in the broadening of the 410 km discontinuity that is as yet unquantified

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

integrated earth resistivity tomography ert and multilevel sampling gas a tool to map geogenic and anthropogenic methane accumulation on brownfield sites soil gas emissions of methane and carbon dioxide on brownfield sites are usually attributed to anthropogenic activities however geogenic sources of soil gas are often not considered during site investigation and risk management strategies this paper presents a field study at a redeveloped brownfield site on a flood plain to identify accumulations of methane biogas trapped in underlying sediments the investigation is based on a multidisciplinary approach using direct multi level sampling measurements and earth resistivity tomography resistivity imaging was applied to evaluate the feasibility of identifying the size and spatial continuity of soil gas accumulations in anthropogenic and naturally occurring deposits as a result biogas accumulations are described within both anthropogenic deposits and pristine organic sediments this result is important to identify the correct approaches to identify and manage risks associated with soil gas emissions on brownfield and pristine sites the organic rich sediments in quaternary fluvial environments of sao paulo basin in particular the tiete river biogas reservoirs can be generated and trapped beneath geogenic and anthropogenic layers potentially requiring the management of brownfield developments across this region