petrographic and geochemical analysis of caliche profiles in a bahamian pleistocene dune two caliche profiles from a pleistocene carbonate dune on san salvador island bahamas were examined by petrographic and geochemical analysis profile a is an immature buried caliche profile characterized by caliche pisolites a friable crust and abundant cerion profile b is a more well developed caliche profile at the top of the dune which contains abundant pisolites rhizomorphs laminated calcrete a breccia and abundant cerion geochemical changes in caliche profiles relative to the host rock are an increase in al2o3 fe2o3 and total organic carbon a decrease in mg and sr and a decrease in 13ccarb 18ocarb and 13corg the magnitude of these changes is probably a function of the duration of subaerial exposure and resultant colonization by dune plants and associated microflora abundance of calcified filaments and needle fibre crystals in profile a attests to the importance of microbial processes in the early development of caliche profiles biogenic structures are largely destroyed in profile b due to recrystallization but indirect evidence of biological activity is retained in the form of carbon isotope values

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

magnetic study of large apollo samples possible evidence for an ancient centered dipolar field on the moon abstract we present new rock magnetic and paleomagnetic results obtained from seventeen apollo samples measurements of the magnetic properties of the samples confirm that the magnetic properties of lunar rocks are dominated by about 0 1 wt of multidomain feni grains the ferromagnetic mineral assemblage is to the first order the same in all lunar lithologies with higher concentration in basalts than in anorthosites some of which are diamagnetic impact processing leads to an increase of the ferromagnetic content out of the seventeen samples eleven show at least one stable component of natural remanent magnetization in some cases this magnetization may be a magnetic contamination however five basalt samples have a component of magnetization that may have recorded a lunar paleofield acquired on the moon for these samples plus two similar samples from a previous study using the rock magnetic fabric as a paleohorizontal proxy paleoinclinations can be estimated from the paleomagnetic data these paleoinclinations are best explained with a dipolar field and a magnetic paleopole located at 75 n therefore our results suggest the existence on the moon at least between 3 8 and 3 3 ga of a dipolar field whose axis is close to the present day rotation axis of the moon the estimated surface field intensities of several tens of t support previous result that the moon had a dynamo field in the past and the proposed paleofield geometry suggests that this dynamo was centered on the lunar present day rotation axis

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

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

magnetic properties of lunar materials meteorites luna and apollo returned samples abstract we present the first comprehensive study of the magnetic properties of lunar meteorites and compare them with measurements from apollo and luna returned samples 37 unpaired lunar meteorites were studied while new susceptibility measurements were performed on 88 luna soil and rock samples to complement published luna and apollo data new magnetic data were also obtained on 4 apollo mare basalt samples magnetic susceptibility and saturation remanence appear mainly controlled by the amount of metallic iron added by the regolith forming processes and meteoritic contamination as shown by a positive correlation with ni and ir content a decrease with depth in regolith core profiles and a decrease with increasing soil size fraction the three sources of lunar materials provide coherent range of magnetic properties although the much larger abundance of anorthositic highland samples in the meteorite collection allows one to better describe the properties of this major lunar lithology the observed range of saturation remanence implies that mare basalts cannot contribute significantly to the patchy lunar crustal magnetizations which must be attributed to superficial impact processed feldspathic or mafic lithologies

lunar paleointensity measurements implications for lunar magnetic evolution abstract we analyze published and new paleointensity data from apollo samples to reexamine the hypothesis of an early 3 9 3 6 ga lunar dynamo our new paleointensity experiments on four samples use modern absolute and relative measurement techniques with ages ranging from 3 3 to 4 3 ga bracketing the putative period of an ancient lunar field samples 60015 anorthosite and 76535 troctolite failed during absolute paleointensity experiments samples 72215 and 62235 impact breccias recorded a complicated multi component magnetic history that includes a low temperature 500 c component associated with a low intensity 2 t similar multi component behavior has been observed in several published absolute intensity experiments on lunar samples additional material from 72215 and 62235 was subjected to a relative paleointensity experiment a saturation isothermal remanent magnetization or sirm experiment neither sample provided unambiguous evidence for a thermal origin of the recorded remanent magnetization we test several magnetization scenarios in an attempt to explain the complex magnetization recorded in lunar samples specifically an overprint from exposure to a small magnetic field an isothermal remanent magnetization results in multi component behavior similar to absolute paleointensity results from which we could not recover the correct magnitude of the original thermal remanent magnetization in light of these new experiments and a thorough re evaluation of existing paleointensity measurements we conclude that although some samples with ages of 3 6 to 3 9 ga are strongly magnetized and sometimes exhibit stable directional behavior it has not been demonstrated that these observations indicate a primary thermal remanence particularly problematic in the interpretation of lunar sample magnetizations are the effects of shock as relative paleointensity measurements for lunar samples are calibrated using absolute paleointensities the lack of acceptable absolute paleointensity measurements renders the interpretation of relative paleointensity measurements unreliable consequently current paleointensity measurements do not support the existence of a 3 9 3 6 ga lunar dynamo with 100 t surface fields a result that is in better agreement with satellite measurements of crustal magnetism and that presents fewer challenges for thermal evolution and dynamo models

stable isotopic composition of an evaporite dissolution breccia in the lower visean limestones of se belgium an evaporitic dissolution breccia occurs in the lower visean limestones of southeastern belgium three periods of brecciation have been recognized the first of which took place early in the diagenetic history the breccia matrix consists of infiltrated marine sediments the fragments and the sedimentary matrix subsequently neomorphosed and lithified in meteoric waters multiple water rock interactions in an open system caused an oxygen isotopic composition of the limestones in equilibrium with meteoric water this composition varies between 8 9 and 5 5 depending on the palaeogeographical position the early diagenetic interaction led also to a spread in the carbon isotopic composition which ranges between an early visean marine 13c 4 pbd and a palaeosol 13c 3 pdb isotopic composition due to the migration of fluids along fractures in the subsurface a second dissolution brecciation and cementation period occurred during this period breccia fragments and the early diagenetic matrix locally neomorphosed a second time the oxygen isotopic composition of the limestone constituents decreased due to the interaction with burial fluids the 18o composition of the breccia fragments and matrix moved towards those of dull orange brown luminescent calcite cements 18o 20 to 11 pdb filling the secondary cavities a third period of brecciation and neomorphism caused the development of orange yellow zoned and bright luminescent microsparites to sparites and of granular to blocky calcites

equatorial aridity and climatic oscillations during the early carboniferous southern britain evidence from palaeosols palaeokarsts and styles of meteoric diagenesis shows that the early carboniferous climate of southern britain was dominantly seasonally semi arid this semi aridity occurred while the region was in an equatorial palaeolatitudinal position the cause of the seasonal aridity was possibly the deflection of easterly winds into a major low pressure zone set up over gondwana during the southern hemisphere summer

origins of some early carboniferous calcrete fabrics revealed by cathodoluminescence implications for interpreting the sites of calcrete formation abstract calcretes from the lower carboniferous marginal marine limestones of south wales germany and belgium exhibit complex calcite microspar fabrics with rhombic irregular and spherical crystals in variable mosaics while many of these fabrics resemble classic recrystallization microspars having irregular crystal forms and non planar crystal boundaries cathodoluminescence microscopy reveals that they result from multiple phases of precipitation and dissolution no evidence for recrystallization by crystal boundary migration or replacement during the transformation of less stable calcite minerals aragonite or high magnesian calcite is seen identical microspar fabrics have been widely described in quaternary calcareous soils which may also be primary fabrics and not due to recrystallization or mineral transformation cathodoluminescence provides a useful tool for interpreting calcrete fabrics and in the case of these carboniferous forms indicates multiple phases of carbonate saturation and leaching reflecting the prominent wetting and drying phases evidenced by associated vertic soils horizons the complex cycles of precipitation and dissolution are characteristic of pedogenic calcretes and the recognition of such features using cathodoluminescence may provide a means of differentiating pedogenic from groundwater calcretes

the lunar dynamo background it is unknown whether the moon has a fully differentiated and melted structure with a metallic core or retains a partially primordial unmelted interior the differentiation history of the moon is manifested by its record of past magnetism paleomagnetism although the moon today does not have a global magnetic field the discovery of remanent magnetization in lunar rocks and in the lunar crust demonstrated that there was a substantial lunar surface field billions of years ago however the origin intensity and lifetime of this field have been uncertain as a result it has been unclear whether this magnetization was produced by a dynamo in the moon s advecting metallic core or by fields generated externally to the moon establishing whether the moon formed a core dynamo would have major implications for understanding its interior structure thermal history and mechanism of formation as well for our understanding of the physics of planetary magnetic field generation the interior structure of the moon and the lunar dynamo new magnetic measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its advecting liquid metallic core innermost red shell this dynamo may have been driven by convection possibly powered by crystallization of the core innermost red sphere and or stirring from the solid mantle thick green shell the magnetic field was recorded as magnetization by rocks on the lunar surface image created by hernan canellas the interior structure of the moon and the lunar dynamo new magnetic measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its advecting liquid metallic core innermost red shell this dynamo may have been driven by convection possibly powered by crystallization of the core innermost red sphere and or stirring from the solid mantle thick green shell the magnetic field was recorded as magnetization by rocks on the lunar surface image created by hernan canellas advances a new generation of laboratory magnetic studies of lunar rocks and spacecraft measurements of lunar crustal magnetic fields have produced major advances in our understanding of the evolution of ancient magnetic fields on the moon it has now been established that a dynamo magnetic field likely existed on the moon from at least 4 5 billion to 3 56 billion years ago with an intensity similar to that at the surface of earth today the field then declined by at least an order of magnitude by 3 3 billion years ago the early epoch of high field intensities may require an exceptionally energetic power source such as mechanical stirring from mantle precession the extended history of the lunar dynamo appears to demand long lived power sources such as mantle precession and core crystallization outlook measurements of the intensity of the ancient lunar dynamo have shown that it was surprisingly intense and long lived the next phase of lunar magnetic exploration will be to obtain more accurate measurements of field paleointensities and to determine when the dynamo initiated and finally disappeared this will be coupled with the continued development of magnetohydrodynamic models for characterizing mechanical and other unusual dynamo mechanisms and further investigations into the thermal structural and geodynamical history of the lunar core and mantle the eventual availability of absolutely oriented samples and in situ spacecraft measurements of bedrock should enable the first measurements of the paleo orientation of lunar magnetic fields such directional data could determine the lunar field s geometry and reversal frequency as well as constrain ancient local and global scale tectonic events

magnetic fidelity of lunar samples and implications for an ancient core dynamo abstract some lunar rocks have stable magnetizations that provide compelling evidence for an ancient lunar core dynamo however a longstanding problem has been interpreting the unstable alternating field af demagnetization behavior observed in the remaining majority of the apollo lunar sample suite similar unstable behavior has also been observed for many meteorites it is unclear whether the behavior of these samples indicates that they formed in the absence of an ancient magnetizing field or whether they simply have poor magnetic recording properties it is necessary to distinguish between these two possibilities in order to determine whether paleomagnetic fields were present on a sample s parent body to address this issue we analyzed five samples whose rock magnetic properties span the full suite of observed demagnetization behaviors mare basalts 15556 15016 12017 10020 and troctolite 76535 we demonstrate that the effects of spurious anhysteretic remanent magnetization arm during af demagnetization in combination with multidomain magnetic carriers and magnetic remanence anisotropy are likely responsible for the apparently poor magnetic behavior of many lunar samples therefore the unstable af demagnetization behavior observed for many lunar samples is not alone sufficient for ruling out the presence of an ancient lunar core dynamo nevertheless spurious arm may explain the observation of surprisingly high 1 t apollo era paleointensity measurements for samples thought to have formed after the cessation of a lunar core dynamo

columnar calcites as testimony of diagenetic overprinting at the boundary between upper tournaisian dolomites and limestones belgium multiple origins for apparently similar features in topographic flat areas sedimentary settings may vary from one outcrop to another in these settings calcite precipitates may yield macroscopically similar columnar features although they are products of different sedimentary or diagenetic processes three columnar calcite crystal fabrics i e rosettes palisade crusts and macro columnar crystal fans have been differentiated near and at the contact between upper tournaisian dolomites and limestones along the southern margin of the brabant wales palaeohigh their petrographic characteristics and geochemical and fluid inclusion data provide information on the dia genetic processes involved rosettes composed of non luminescent columnar calcite crystal fans 1 5 cm in diameter developed on top of one another forming discrete horizons in repetitive sedimentary cycles the cycles consist of three horizons i a basal horizon with fragments from the underlying horizon ii a micrite microspar horizon with incipient glaebules iii an upper horizon consisting of calcite rosettes with desiccation features the petrographical features and 18o signatures of 10 0 to 5 5 and 13c values of 5 5 to 3 2 support either evaporative growth an evaporative pedogenic origin or overprinting of marine precipitates palisade crusts composed of a few to 10 mm long nonluminescent calcite crystals coat palaeokarst cavities successive palisade growth stages occur which are separated by thin laminae of micrite or detrital quartz displaying a geopetal arrangement palisade crusts are interpreted as intra mississippian speleothems this interpretation is supported by their petrographic characteristics and isotopic signature 18o 8 7 to 6 5 and 13 4 8 to 2 5 macro columnar crystals 1 50 cm long developed mainly perpendicular to cavity walls and dolomite clasts crystal growth stages in the macro columnar crystals are missing 18o values vary between 6 4 and 6 8 and 13c values between 5 2 and 0 9 these features possibly support a late diagenetic high temperature precipitation in relation to hydrothermal karstification 2005 international association of sedimentologist

the diagenesis of the late dinantian derbyshire east midland carbonate shelf central england carbonate cements in late dinantian asbian and brigantian limestones of the derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement the sequence is documented using cement petrography cathodoluminescence trace element geochemistry and c and o isotopes the earliest cements pre zone 1 are locally developed non luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes they contain negligible fe mn and sr but up to 1000 ppm mg their isotopic compositions centre around 18o 8 5 13c 5 0 calcretes contain less 13c subsequent cements are widespread as inclusion free low mg low fe crinoid overgrowths and are described as having a dead bright dull cathodoluminescence the dead cements zone 1 are mostly non luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres across dead bright subzones there is a clear trend in mg 500 900 ppm mn 100 450 ppm and fe 80 230 ppm zone 1 cements have isotopic compositions centred around 18o 8 0 and 13c 2 5 zone 2 cement is bright thin and complexly subzoned it is geochemically similar to bright subzones of zone 1 cements dull zone 3 cement pre dates pressure dissolution and fills 70 or more of the pore space it generally contains little mn fe and sr but can have more than 1000 ppm mg increasing stratigraphically upwards the 18o compositions range from 5 5 to 15 and the 13c range is 1 to 3 20 00 zone 4 fills veins and stylolite seams in addition to pores it is synchronous with pb ba f ore mineralization and oil migration zone 4 is ferroan with around 500 ppm fe up to 2500 ppm mg and up to 1500 ppm mn isotopic compositions range widely 15o 2 7 to 9 and 13c 3 8 to 2 50 unaltered marine brachiopods suggest a dinantian seawater composition around 15o 0 smow but vital isotopic effects probably mask the original 13c pdb value pre zone 1 calcites are meteoric vadose cements with light soil derived 13c and light meteoric 18o an unusually fractionated pluvial 15o smow value of around 6 is indicated for local dinantian meteoric water calcrete 18o values are heavier through evaporation zone 1 textures and geochemistry indicate a meteoric phreatic environment fe and mn trends in the bright subzones indicate stagnation and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies meteoric alteration of the rock body was pervasive by the end of zone 1 with a general resetting of isotopic values zone 3 is volumetrically important and external sources of water and carbonate are required emplacement was during the namurian early westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the derbyshire east midland shelf the light 18o values mainly reflect burial temperatures and an unusually high local heat flow but an input of highly fractionated hinterland derived meteoric water at the unconformity is also likely relatively heavy 13c values reflect the less altered state of the source carbonate and aquifer zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism light organic matter derived 13c and heavy 18o values suggest basin derived formation water combined with textural evidence of geopressures this relates to local high temperature ore mineralization and oil migration low water to rock ratios with host rock buffering probably affected the final isotopic compositions of zone 4 masking extremes both of temperature and organic matter derived co2

an impact driven dynamo for the early moon recent palaeomagnetic and seismological studies have strengthened the suggestion that the moon once possessed a core dynamo despite its importance as a constraint on lunar evolution there is currently no consensus on how such a dynamo was driven two groups working independently have arrived at the idea that the lunar dynamo was powered by mechanical stirring of the liquid core dwyer et al investigate the mechanism of a dynamo driven by continuous mechanical stirring arising from the differential motion between the solid silicate mantle and the liquid core beneath they show that the fluid motions and the power required to drive a dynamo operating continuously for more than 1 billion years are readily obtained by such mechanical stirring le bars et al propose a model whereby the dynamo action comes from impact induced changes in the moon s rotation rate they show that basin forming impact events are energetic enough to have unlocked the moon from synchronous rotation and that the subsequent large scale fluid flows in the core excited by the tidal distortion of the core mantle boundary could have powered a lunar dynamo the origin of lunar magnetic anomalies1 2 3 4 5 remains unresolved after their discovery more than four decades ago a commonly invoked hypothesis is that the moon might once have possessed a thermally driven core dynamo3 but this theory is problematical given the small size of the core and the required surface magnetic field strengths6 an alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins7 but many magnetic anomalies exist that are not associated with basin antipodes here we propose a new model for magnetic field generation in which dynamo action comes from impact induced changes in the moon s rotation rate basin forming impact events are energetic enough to have unlocked the moon from synchronous rotation8 and we demonstrate that the subsequent large scale fluid flows in the core excited by the tidal distortion of the core mantle boundary9 could have powered a lunar dynamo predicted surface magnetic field strengths are on the order of several microteslas consistent with palaeomagnetic measurements5 and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins

geologic constraints on the glacial amplification of phanerozoic climate sensitivity the long term carbon cycle depends on many feedbacks silicate weathering consumes atmospheric co2 but is also enhanced by the increased temperatures brought about by this important greenhouse gas the long term sensitivity t2x of climate to co2 doubling modulates the strength of this negative feedback we update the model experiment of royer and others 2007 by estimating an empirical probability density function pdf of t2x for the phanerozoic by using an improved geocarbsulf carbon cycle model to predict a larger recalibrated set of proxy co2 measurements from the present day to 420 ma the new geocarbsulf parameterizes the rapid weathering of volcanic rocks relative to plutonic rocks updates to the carbon cycle model and the proxy co2 data set induce opposing model responses as a result our experiment maintains an agreement with t2x estimates based on numerical climate models and late cenozoic paleoclimate for a climate sensitivity t2x that is uniform throughout the phanerozoic the most probable value is 3 to 4 c geocarbsulf fits the proxy co2 data equally well and with far more parameter choices if t2x is amplified by at least a factor of two during the glacial intervals of the paleozoic 260 340 ma and cenozoic 0 40 ma relative to non glacial intervals of earth history for glacial amplification of two the empirical pdfs for glacial climate sensitivity predict t2x g 2 0 c with 99 percent probability t2x g 3 4 c with 95 percent probability and t2x g 4 4 c with 90 percent probability the most probable values are t2x g 6 to 8 c this result supports the notion that the response of earth9s present day surface temperature will be amplified by the millennial and longer term waxing and waning of ice sheets

a survey of the natural remanent magnetization and magnetic susceptibility of apollo whole rocks abstract magnetic properties of lunar rocks may help understand the evolution of the past magnetic field of the moon however these properties are often measured on small subsamples which may not be representative of the bulk lunar rocks in this study a rough magnetic characterization of a large fraction of the apollo collection was performed using non destructive methods with a focus on large samples mean mass 500 g the natural remanent magnetization of 123 apollo samples and the magnetic susceptibility of 154 apollo samples were measured in the apollo storage vault at the lunar sample laboratory facility in houston magnetic susceptibility is strongly controlled by lithology and is clearly enhanced by impact processing and associated incorporation of meteoritic metal as well as formation of nanometric iron particles by space weathering the natural remanent magnetization is lower by a factor of 3 than that measured on small samples 100 mg suggesting magnetic contamination during small sample preparation or handling or directional heterogeneity in remanence within large samples the ratio of natural remanence magnetization to magnetic susceptibility may be used as selection tool for further paleomagnetic study it is a crude paleointensity proxy and its overall temporal evolution is coherent with the existence of a high magnetic field from 4 ga to 3 5 ga and a subsequent weaker field epoch as previously defined in the literature our data also raise the possibility that the intensity of the paleomagnetic field during the high field epoch may have been more variable and lower on average than previously suggested

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

a long lived lunar dynamo powered by core crystallization the moon does not possess an internally generated magnetic field at the present day but extensive evidence shows that such a field existed between at least 4 2 and 3 56 ga ago the existence of a metallic lunar core is now firmly established and we investigate the influence of inner core growth on generating a lunar core dynamo we couple the results of a 3 d spherical thermochemical convection model of the lunar mantle to a 1 d thermodynamic model of its core the energy and entropy budget of the core are computed to determine the inner core growth rate and its efficiency to power a dynamo sulfur is considered to be the main alloying element and we investigate how different sulfur abundances and initial core temperatures affect the model outcomes for reasonable initial conditions a solid inner core between 100 and 200 km is always produced during its growth a surface magnetic field of about 0 3 t is generated and is predicted to last several billion years though most simulations predict the existence of a core dynamo at the present day one way to stop magnetic field generation when the inner core is growing is by a transition between a bottom up and top down core crystallization scheme when the sulfur content becomes high enough in the outer core according to this hypothesis a model with about 6 to 8 wt sulfur in the core would produce a 120 160 km inner core and explain the timing of the lunar dynamo as constrained by paleomagnetic data

stable isotope signatures associated with palaeosols pennsylvanian holder formation new mexico the holder formation pennsylvanian virgilian of southern new mexico usa consists of limestones interbedded with siliciclastics it was deposited during times of glacio eustatic sea level change and was exposed subaerially during multiple sea level lowstands microcomponents and whole rock samples of limestones were analysed for 13c and 18o values to examine the method of whole rock isotopic analysis for detecting subaerial exposure events and to determine the diagenetic processes acting during subaerial exposure whole rock isotopic shifts are not consistently present across petrographically identified subaerial exposure surfaces apparently whole rock isotopic shifts do not result from wholesale replacement of the host sediment during soil formation however the isotopic shifts are present in calcareous soil precipitated microcomponents such as rhizoliths laminated crusts and soil precipitated cements the components are heterogeneous in isotopic composition but converge on a meteoric calcite line at about 18o 5 5 these microcomponents are heterogeneous in distribution and may either dominate or be a minor constituent of the whole rock at a single stratigraphic horizon without petrographic selection of palaeosol components the detection of whole rock isotopic shifts may depend on the selection or chance sampling of a rock containing abundant microcomponents precipitated in a soil environment only minor whole rock isotopic shifts come from those rocks bearing no evidence of exposure and bearing lithological characteristics suggesting subaerial exposure was unlikely

characteristics genesis and parameters controlling the development of a large stratabound htd body at matienzo ramales platform basque cantabrian basin northern spain abstract at matienzo basque cantabrian basin northern spain a large stratabound htd body 4 by 2 km 2 and 80 400 m thick delimited by two parallel sinistral strike slip faults is exposed in aptian carbonates the margins of the htd body are characterised by dolomite tongues indicating that some limestone beds were more prone to dolomitisation however no clear relationship between htd occurrence and precursor limestone facies can be established massive limestone beds as found at the top of the htd body act as barriers to hydrothermal processes since no dolomite is present in or above these beds three types of dolomites have been differentiated i e 1 matrix 2 coarse crystalline and 3 zebra dolomite the distribution of the dolomite types is attributed to ascending fluid flow and changing degree of dolomite oversaturation the dolomite body was formed by two dolomitisation phases under burial conditions no indications for a synsedimentary early diagenetic dolomitisation have been observed the first dolomitisation phase is characterized by ferroan dolomite and the second by non ferroan dolomite the two htd phases are characterised by depleted 18 o values ranging between 10 and 16 v pdb 13 c values similar to the aptian albian marine signature and homogenisation temperatures of primary fluid inclusions between 120 c and 150 c the dolomitising fluid was enriched in 87 sr compared to aptian seawater excluding the latter as an unmodified fluid source for dolomitisation microthermometry of primary fluid inclusions indicates that the dolomitising fluid evolved from a moderate saline 9 7 14 0 wt nacl to a more saline 10 9 21 0 wt nacl h 2 o nacl brine the dolomitising fluid likely originated from evaporated seawater fluid circulation through the dolomitised strata is inferred to have taken place during the tectonically active period of the late albian throughout which important sinistral strike slip movements along basement faults occurred

decline of the lunar core dynamo abstract recent analyses of apollo samples have demonstrated that a core dynamo existed on the moon between at least 4 25 and 3 56 billion years ago ga with surface field intensities reaching 70 t however it is unknown when the moon s magnetic field declined determining the temporal evolution of the dynamo is important because it constrains secular changes in power at the lunar core mantle boundary and by implication the moon s thermal and orbital evolution and the field generation mechanism here we present paleomagnetic data from several younger mare basalts which demonstrate that the surface magnetic field had declined precipitously to 4 t by 3 19 ga it is currently unclear whether such a rapid decrease in field strength reflects either the cessation of the dynamo during this period or its persistence beyond 3 19 ga in a drastically weakened state

carbon dioxide in the paleozoic atmosphere evidence from carbon isotope compositions of pedogenic carbonate stable carbon isotope compositions of pedogenic carbonate occurring in three clay rich vertic paleosols within paleozoic red bed successions in central pennsylvania provide a record of past pedogenic environments and can be used to estimate co sub 2 pressure p sub co sub 2 of the paleozoic atmosphere the delta sup 13 c values of carbonate nodules from paleosols in the deltaic lower bloomsburg formation upper silurian reflect the contribution of carbon from marine groundwater or fossils coupled with low biological activity the delta sup 13 c values of carbonate rhizocretions from stratigraphically high paleosols in the bloomsburg formation and in the alluvial catskill upper devonian and mauch chunk upper mississippian formations suggest an extensive c sub 3 flora and significant contribution of atmospheric co sub 2 paleozoic atmospheric co sub 2 levels inferred from delta sup 13 c of pedogenic carbonate are significantly higher than present levels

the oxygen and carbon isotope composition of carboniferous fossil components sea water effects the aragonitic molluscs and lime mud of the pennsylvanian buckhorn asphalt deese group of southern oklahoma precipitated calcium carbonate in oxygen and carbon isotopic equilibrium with ambient sea water in addition 18o values indicate that the pelecypods precipitated their shells during the warmer months of the year the coiled nautiloids probably precipitated their shells in the warm surface water and throughout the year for the orthocone nautiloids the 18o values suggest that they precipitated their shells in deeper cooler water the low mg calcite brachiopods of the mississippian lake valley formation of new mexico precipitated shells in oxygen and carbon isotopic equilibrium with ambient sea water the 18o and 13c values of the buckhorn and lake valley faunas in conjunction with other published results suggest that carboniferous sea water was on a average depleted in 18o by 1 5 2 pdb relative to recent sea water however the 13c value of 2 6 2 pdb for average carboniferous sea water is similar to that of recent ocean water early diagenetic alteration of metastable carbonates probably occurs in a meteoric sea water mixing zone in this zone the oxygen and carbon isotopic compositions of these components are increased by about 2 4 pdb over their marine composition

a long lived lunar core dynamo paleomagnetic measurements indicate that a core dynamo probably existed on the moon 4 2 billion years ago however the subsequent history of the lunar core dynamo is unknown here we report paleomagnetic petrologic and 40ar 39ar thermochronometry measurements on the 3 7 billion year old mare basalt sample 10020 this sample contains a high coercivity magnetization acquired in a stable field of at least 12 microteslas these data extend the known lifetime of the lunar dynamo by 500 million years such a long lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior the inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

stable isotopic composition of paleosols in the lower visean of eastern belgium evidence of evaporation and soil gas co2 abstract numerous paleosols occur in the lower visean peritidal limestones of eastern belgium at the top of the peritidal unit a widespread paleosol horizon occurs which has been analysed for its carbon and oxygen isotopic composition in spite of the paleozoic age of the pedogenic carbonates the influence of evaporation and soil gas co 2 on the stable isotopic composition of the paleosol is very pronounced this has been assinged to the long exposure time in a semi arid seasonal climate evaporation caused an enrichment in 18 o in the paleosol compared with the over and underlying limestones which were cemented and mineralogically stabilized in meteoric pore waters the influence of soil gas co 2 in the soil formation is clearly indicated by the depletion in 13 c of the pedogenic carbonates 13 c 5 pdb compared with the carbon isotopic composition of lower visean marine limestones 13 c 4 pdb the possible effect of carbon derived from atmospheric co 2 on the 13 c values of the paleosols is discussed

persistence and origin of the lunar core dynamo the lifetime of the ancient lunar core dynamo has implications for its power source and the mechanism of field generation here we report analyses of two 3 56 gy old mare basalts demonstrating that they were magnetized in a stable and surprisingly intense dynamo magnetic field of at least 13 t these data extend the known lifetime of the lunar dynamo by 160 my and indicate that the field was likely continuously active until well after the final large basin forming impact this likely excludes impact driven changes in rotation rate as the source of the dynamo at this time in lunar history rather our results require a persistent power source like precession of the lunar mantle or a compositional convection dynamo

global prevalence of double benioff zones double benioff zones provide opportunities for insight into seismogenesis because the underlying mechanism must explain two layers of deep earthquakes and the separation between them we characterize layer separation inside subducting plates with a coordinate rotation to calculate the slab normal distribution of earthquakes benchmark tests on well established examples confirm that layer separation is accurately quantified with global seismicity catalogs alone global analysis reveals double benioff zones in 30 segments including all 16 subduction zones investigated with varying subducting plate ages and stress orientations which implies that they are inherent in subducting plates layer separation increases with age and is more consistent with dehydration of antigorite than chlorite