phosphoran olivine overgrowths implications for multiple impacts to the main group pallasite parent body phosphoran olivine 1 7 wt p2o5 is a metastable phase known from fewer than a dozen meteoritic or terrestrial occurrences we have thoroughly examined phosphoran olivine in the springwater pallasite to characterize its distribution textural relationships and geochemistry phosphoran olivine is abundant in springwater as randomly distributed millimeter scale partial overgrowths on the p free olivine crystals geochemical analyses support the substitution mechanism of p into the tetrahedral si site with octahedral site vacancies for charge balance observed trace element variations on the other hand are not related to p substitution element mapping reveals fine scale oscillatory p zoning in unusual serrate patterns indicating rapid crystal nucleation from a melt as proposed by boesenberg and hewins 2010 and a subsequently variable rate of crystallization the timing of phosphoran olivine formation in springwater is constrained to after the period of macroscopic olivine rounding but before the cooling of the metal matrix because the phosphoran overgrowths overprint specific host grain boundary modifications we suggest that the episode of extremely rapid cooling necessary to crystallize and preserve this rare phase may have been triggered by an additional impact to the parent body

activation volume of si diffusion in san carlos olivine implications for upper mantle rheology the effect of pressure on silicon diffusion in san carlos olivine has been determined using a uniaxial split sphere apparatus ussa 2000 and the nuclear reaction analysis technique nra on the 30si isotope experiments were performed at high temperature t 1763 k and pressures between 4 and 9 gpa the specimens were inserted into a pure fe capsule which is very effective in maintaining the oxygen fugacity within the stability field of olivine as well as providing a soft medium to mechanically protect the crystals diffusion profiles along the b crystallographic axis and of characteristic length of the order of 50 nm were obtained after annealing the olivine samples between 1 and 4 hours we find the activation volume for silicon diffusion in san carlos olivine to be vsi 0 7 2 3 10 6 m3 mol after a correction for oxygen fugacity which is pressure dependent this result demonstrates that pressure has practically no effect upon silicon diffusion under our temperature and pressure conditions extrapolation of our high pressure measurements to 1 atm gives a si diffusion coefficient log dsi 18 9 1 0 with dsi in m2 s finally our experiments show that according to the point defect model of jaoul 1990 the activation volume for creep of olivine at high temperature is dominated by the effect of pressure on the mg defect concentration and has an activation volume close to 6 10 6 m3 mol

aligned olivine in the springwater pallasite the mechanism by which olivine grains became embedded within iron nickel alloy in pallasite meteorites continues to be a matter of scientific debate geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals however little research attention has been devoted to their crystallographic orientations within the metal matrix using electron backscatter diffraction we have collected crystallographic orientation data for 296 crystals within 65 cm2 sample surface from springwater though no global crystallographic preferred orientation exists very low misorientations are observed among 100 axes of olivine crystals within specific texturally defined domains combined with a thorough characterization of large scale springwater textures the definitively nonrandom spatial distribution of olivine orientations provides clues regarding the nature of the olivine s initial formation environment as well as the sequence of events subsequent to metal incorporation

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

surface wave focusing and acoustic communications in the surf zone the forward scattering of acoustic signals off of shoaling surface gravity waves in the surf zone results in a time varying channel impulse response that is characterized by intense rapidly fluctuating arrivals in some cases the acoustic focusing by the curvature of the wave crest results in the formation of caustics at or near a receiver location this focusing and the resulting caustics present challenges to the reliable operation of phase coherent underwater acoustic communications systems that must implicitly or explicitly track the fluctuations in the impulse response the propagation physics leading to focusing are studied with both experimental data and a propagation model using surface wave profiles measured during the collection of the experimental data the deterministic experimental and modeled data show good agreement and demonstrate the stages of the focusing event and the impact of the high intensity arrivals and rapid fluctuations on the ability of an algorithm to accurately estimate the impulse response the statistical characterization of experimental data shows that the focusing by surface gravity waves results in focused surface reflected arrivals whose intensity often exceeds that of the direct arrival and the focusing and caustic formation adversely impacts the performance of an impulse response estimation algorithm

determination of ocean surface wave shape from forward scattered sound forward scattered sound from the ocean surface is inverted for wave shape during three periods low wind mix of wind and swell and stormy derived wave profiles are spatially limited to a fresnel region at or near the nominal surface specular reflection point in some cases the surface wave profiles exhibit unrealistic temporal and spatial properties to remedy this the spatial gradient of inverted waves is constrained to a maximum slope of 0 88 under this global constraint only surface waves during low wind conditions result in a modeled surface multipath that accurately matches data the power spectral density of the inverted surface wave field saturates around a frequency of 8 hz while upward looking sonar saturates at 1 hz each shows a high frequency spectral slope of 4 that is in agreement with various empirical ocean wave spectra the improved high frequency resolution provided by the scattering inversion indicates that it is possible to remotely gain information about high frequency components of ocean waves the inability of the inversion algorithm to determine physically realistic surface waves in periods of high wind indicates that bubbles and out of plane scattering become important in those operating scenarios

lateglacial and holocene environmental changes in portuguese coastal lagoons 2 microfossil multiproxy reconstruction of the santo andre coastal area benthic foraminiferal ostracod calcareous nannoplankton and diatom assemblages have been analysed from the 25 45 sedimentary succession of a borehole drilled in the santo andre lagoon southwestern portugal the zones and subzones recognized according to their microfossil content have been used to define six palaeoenvironmental stages extending from the lateglacial to the present stage a and the lower part of stage b 14 2 to 10 0 ka represent a postglacial terrestrial environment when sea level was below present following eustatic sea level rise a normal marine open bay environment established during the upper part of stage b 10 0 to 5 4 ka before 5 4 ka a coastal lagoon developed as a consequence of a sandy barrier formation since then natural variation in the permeability of the detrital barrier through time has been the primary control of the physical chemical and biological features of the lagoonal environment during stage c 5 4 to 3 6 ka as a freshwater dominated lagoon stage d 3

chemical signatures of palaeotsunamis a forgotten proxy article i nfo article history a range of diagnostic criteria are required to help identify palaeotsunami deposits although chemical signatures have long been used as indicators of palaeosalinity in sedimentary sequences their use in the studies of palaeotsunami deposits is rarely applied and is yet to be widely recognised the chemical composition of interstitial water in coastal ponds and sedimentary sequences in coastal marshes and lagoons has been used successfullyasanindicatoroftsunamiinundation chemicalsignaturescanalsoprovidecluesaboutthelandward limit of runup of a tsunami beyond the area of sediment deposition like most palaeotsunami proxies however the preservation of chemical signatures varies with environmental conditions

a petrological and chemical reexamination of main group pallasite formation abstract the large number of pallasite parent bodies suggests that their formation was a common event in asteroid evolution new microprobe data has been generated for pallasite olivines and chromites that indicate subsolidus redox processes while literature data has been collated and correlated to form new results and interpretations the new data include information on metal compositions the metal cooling rates the formation of round and fragmental olivine the close packing of olivine the crystallization of the phosphates phosphoran olivine and orthopyroxene and the bulk pallasite p and s contents a model for main group pallasites has been developed using fractional melting of a chondritic precursor to make a multi layered parent body one portion of this contains a gradational metal olivine pallasite texture concentric downward crystallization of the molten metal is indicated based on cooling rates and metal compositions fractional crystallization of the residual silicate and metallic melts produces the minor phases on cooling comparisons to and a brief review of past models particularly those utilizing mixing have been made

microfacies characteristics of a tropical mangrove fringed shoreline cleveland bay queensland australia sedimentary and taphonomic controls on mangrove facies development mangrove ecosystems strongly influence the sedimentology and geomorphology of contemporary intertidal environments and are known to have occupied similar ecological niches at least as far back as the early cenozoic given this it is remarkable how few records of mangrove occurrence have been reported in the geologic record here a microfacies approach is adopted to examine the characteristics of a contemporary mangrove colonized intertidal succession along an active prograding shoreline in north queensland australia and compared with a proximal mid late holocene preserved intertidal succession this enables a comparison of microfacies development and preservation potential in like for like depositional environments over short temporal and spatial scales in the contemporary intertidal system active shoreline progradation has produced a highly gradational shallowing upward succession mid to low intertidal substrates characterized by an abundant and diverse bioclast especially molluscan fauna and a rich calcareous foraminiferal assemblage are overlain by organic rich upper intertidal mangrove facies characterized by abundant organic material especially wood and bark fragments and a distinct fauna of agglutinated foraminifera the major sedimentary effects of mangrove progradation are to introduce substantial amounts of organic matter into the substrate effectively overprinting the mudflat facies to mix and re texture due to root network development and infaunal bioturbation the sediment substrate and to modify the depth ranges over which infaunal molluscs and foraminifera occur variations in the relative abundance of constituents permit however the clear delineation of mangrove and intertidal mudflat facies whilst an essentially similar facies succession is identifiable in the sub recent many of the diagnostic facies constituents are either not preserved or are present in far lower abundances than in the modern in particular the inferred mangrove units contain far less organic material most wood and root material is absent are essentially devoid of bioclastic material and contain a depauperate agglutinated foraminiferal fauna the primary drivers of this are 1 loss of calcareous foraminifera and bioclasts due to carbonate dissolution 2 loss of agglutinated foraminifera due primarily to biological fiddler crab test degradation and mineralization of their organic binding agents and 3 aerobic and anaerobic degradation of organic material consequently actual criteria for identifying the presence of a former mangrove in this succession are limited such poor preservation even within sub recent mangrove deposits suggest that the longer term preservation potential of key diagnostic criteria is likely to be extremely poor within similar terrigenoclastic dominated organically enriched successions thus whilst mangroves significantly modify and re texture intertidal substrates use may often need to be made of sparsely preserved faunal or floral remains or traces interpreted in the context of the broader intertidal depositional succession to infer the presence of mangrove colonized substrates in the rock record

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

simulations of acoustic tomography array performance with untracked or drifting sources and receivers ocean tomography as originally proposed required all sources and recievers to be tautly moored and acoustically tracked to separate travel time perturbations due to mooring motion from those due to ocean features it is possible to process the tomographic travel times to estimate both ocean sound speed perturbations and mooring offsets effecting a separation without external tracking a side effect of this processing is a check on the ray identification since the varying instrument positions can be used as a synthetic array for estimating ray angle simulations and examples with actual data were used to contrast mapping performance with and without mooring tracking for a variety of ray data sets in general the ocean maps degrade when the tracking data are withheld however when many high precision ray travel time measurements are available the degradation is small in these cases it would be possible to deploy free drifting instruments as part of a monitoring experiment

re os systematics in pallasite and mesosiderite metal re os data on pallasite metal yield a sufficient range in re os to permit the determination of a whole rock isochron if pallasites from different groups are considered together the results are indistinguishable from the data obtained on groups iab iiab iid iiiab iva and ivb iron meteorites pallasite data were obtained on samples of the main group which have been considered related to group iiiab irons and on samples of the distinctive pallasites eagle station finmarken and marjalahti it appears that iron meteorites and pallasites crystallized within a time interval of 20 ma this result is consistent with the evidence from the short lived chronometers 107 pd 107 ag and 53 mn 53 cr it is also consistent with the evidence from 182 hf 182 w that the time interval over which molten feni metal from different iron meteorites equilibrated with and became segregated from silicates was 10 ma the well defined 187 re 187 os whole rock isochron for pallasites and iron meteorites requires that they were formed in parent bodies that had been partially molten and segregated feni metal and fes and then all crystallized within a 20 ma time interval this conclusion appears to apply to members of distinct groups of iron meteorites and pallasites which are viewed as not being cogenetic the short time scale requires that the irons and pallasites were formed in small parent planets of 10 km radius or near the surface of larger bodies in contrast to the pallasites we find that feni samples from mesosiderites have a narrow range in re os so that it is not possible to determine a whole rock isochron for these samples the mesosiderite data also lie somewhat displaced from the iron meteorite and pallasite isochron indicating a more complex multi stage evolution based on sm nd data on mesosiderite silicate clasts the re os results on mesosiderite metal are compatible with the model of melted or partially molten feni cores or pods still preserved in protoplanetary bodies when these bodies were disrupted up to 150 ma after early formation and the feni was splashed onto the surfaces of other small differentiated planetesimals

variable response of coastal environments of the northwestern gulf of mexico to sea level rise and climate change implications for future change the results from nearly three decades of marine geological research in the northwestern gulf of mexico are compiled in an effort to understand those factors e g sea level rise sediment supply subsidence antecedent topography that influenced coastal evolution during the last eustatic cycle 120 ka to present armed with this information we evaluate coastal response to variable sea level rise of the holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes the early holocene evolution of northwestern gulf of mexico bays was punctuated by rapid and possibly synchronous flooding events that are interpreted as resulting from episodes of rapid sea level rise two of these events one between 8 4 and 8 0 ka and the other between 7 4 and 6 8 ka were associated with known episodes of ice sheet retreat in north america and antarctica respectively during the middle and late holocene the east texas and western louisiana coasts experienced episodes of stability and growth followed by rapid shoreline retreat while the central texas coast remained relatively stable this variability in coastal response to sea level rise resulted mainly from differences in sediment supply and the highly irregular antecedent topography on which coastal environments formed sand that nourished the evolving east and south texas as well as westernmost louisiana coasts was derived mainly from transgressive ravinement of deltas that were formed during the falling stage of sea level mis5e mis2 the loci of these deltas controlled the spatial variability of this offshore sand supply sand supply to the central texas coast has been dominated by converging longshore currents and throughout the middle to late holocene was large enough to keep pace with sea level rise moreover sand supply from rivers has varied considerably in response to climate change during the early holocene when the average rate of linear sea level rise was 4 2 mm yr the brazos colorado and rio grande rivers all formed deltas on the inner continental shelf today only the brazos contributes enough sediment to the gulf of mexico to form a delta but its sand delivery is minimal a reversal from late holocene growth of western louisiana east texas and south texas barrier islands and peninsulas to erosion occurred during the last 2 0 ka after the rate of sea level rise began to decelerate the actual timing of this reversal was diachronous across the coast and was caused by a decrease in sediment supply once offshore sand sources were bypassed by the landward advancing shoreface transgressive ravinement differences in the exact timing and rate of retreat also reflect variability in the offshore profiles of these barriers and their thickness which results from the underlying relief on the pleistocene surface the late holocene was also the time of chenier plain development in western louisiana and east texas that was marked by localized differences in growth and retreat the current rate of eustatic sea level rise in the northern gulf of mexico is in the range of 2 0 and 3 0 mm yr and is approaching rates of the early holocene this is on average about five times the long term rate of the past 4 0 ka this larger rate is associated with an increase in coastal erosion in historical time relative to long term rates current rates of gulf shoreline erosion are approaching rates of the early to mid holocene and the rate of retreat of some barriers is not sustainable core transects off central texas reflect a late holocene history of shoreface progradation but the modern shoreline is currently eroding albeit at slower rates than elsewhere along the coast overall the sand supply needed to sustain the gulf shoreline is lacking likewise baylines are experiencing erosion rates that are faster than the late holocene average and bayhead deltas are at the tipping point of catastrophic retreat spatial variability in erosion rates highlights the importance of factors such as sediment supply subsidence and anthropogenic influences on coastal evolution tropical storms and hurricanes while exerting the most noticeable coastal change merely exacerbate overall shoreline retreat and migration along the entire northwestern gulf coast the impact of human intervention to natural processes is particularly evident primarily due to alterations in river discharge and sediment supply to the coast interruptions in along shore and cross shore sand transport and increases in rates of subsidence through fluid withdrawal compared to natural changes that took place during the holocene the impacts of human activity have been virtually instantaneous the geological record indicates that the ongoing increase in the rate of sea level rise coupled with diminished sediment supply and human intervention will continue to severely impact the low gradient coastal environments of the northwestern gulf of mexico

sediment accretion and recent sea level rise in the solent southern england inferences from radiometric and geochemical studies abstract a detailed radionuclide and geochemical study has been carried out on recent sediments from the solent estuarine system southern england the vertical distributions of a series of radionuclides 210 pb 137 cs 238 pu 239 240 pu 241 am and 60 co have been examined which provide a measure of the rate of sediment accumulation in southern england estuaries the reliable use of radionuclides as indicators of sediment accumulation depends in part on their chemical immobility lack of redox migration 60 co in particular shows evidence for redox mobilization hence it is essential to use a number of chemically different or inert radionuclides to eliminate possible bias in calculated sediment accumulation rates while local intra estuary effects influence rates of sediment accumulation the main control of vertical saltmarsh growth over the solent area is a rise in mean sea level dating of saltmarsh cores indicates a 4 5 mm year 1 rise in relative sea level over the last 100 years in good agreement with tide gauge data comparison with data from the literature implies that a recent acceleration in sea level rise has occurred from 1 2 mmyear 1 to 4 5 5 mm year 1 possibly due to changes in tidal regime or an acceleration in crustal subsidence

expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami article i nfo some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 indian ocean tsunami and the 2009 south pacific tsunami and a revised toolkit provided the new application of anisotropy of magnetic susceptibility ams to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences together with data from grain size analysis are presented the value of chemical proxies as indicators of saltwater inundation associated marine shell and or coral high energy depositional environment and possible contamination is demonstrated and issues of preservation addressed we also provide new findings from detailed studies of heavy minerals new information gathered during the unesco international oceanographic commission ioc international tsunami survey of fine onshore sediments following the 2009 south pacific tsunami is presented and includes grain size chemical diatom and foraminifera data the tsunami deposit varied ranging from fining upward sand layers to thin sand layers overlain by a thick layer of organic debris and or a mud cap grain size characteristics chemical data and microfossil assemblages provide evidence for marine inundation from near shore and changes in flow dynamics during the tsunami

bromine counts from xrf scanning as an estimate of the marine organic carbon content of sediment cores 1 xrf sediment core scanning technology is increasingly used to quantify sediment composition the overall good correlation between biophilic halogen bromine br and sedimentary total organic carbon toc potentially allows the fast estimation of down core toc profiles by xrf scanning in order to test this approach we present data from the arabian sea and a mediterranean brine basin comparing xrf core scanning br data with discrete sample toc analyses overall br counts and toc show a clear correlation except when stable carbon isotope and c n data indicate intervals characterized by enhanced input of terrestrial organic matter hence solid phase br is exclusively associated with marine organic matter moc and can be used as a direct estimate of this parameter after a calibration is established high pore water br in the brine core steepens the br toc correlation but after salt correction shows a nearly identical gradient to that of the arabian sea core

liquid distribution and attainment of textural equilibrium in a partially molten crystalline system with a high dihedral angle liquid phase the evolution of a high dihedral angle liquid in a crystalline matrix such as fe s melt in an olivine matrix is of vital importance for a range of questions including planetary core mantle differentiation we performed hydrostatic in situ analogue experiments on norcamphor h2o liquid and high temperature experiments on olivine fes melt to investigate the evolution of the liquid and the attainment of textural equilibrium in the liquid and the solid the liquid distribution was dominated by large unconnected liquid pools smaller melt lenses and the regular occurrence of dry three grain triple junctions compared to low dihedral angle systems the liquid pockets had a very low mobility during grain growth and disequilibrium features such as elongated liquid pools only reequilibrated slowly the results have several consequences for the evolving microstructure 1 immobile liquid pockets hinder grain boundary migration and promote abnormal grain growth 2 the attainment of textural equilibrium in solid liquid regions is delayed with respect to liquid free regions 3 grain growth does not promote liquid pocket growth as in low dihedral angle systems and liquid pockets do not directly interact with each other during annealing 4 an existing liquid network is unstable and pinches off in the long term even if the liquid fraction is above the theoretical percolation threshold with regard to this final point percolative core mantle differentiation through an interconnected melt network may not be a viable mechanism even above the suggested percolation threshold of 5 vol

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

massive chromite in the brenham pallasite and the fractionation of cr during the crystallization of asteroidal cores abstract large 2 mm chromite grains are present in iiiab iron meteorites and in the main group pallasites pmg closely related to high au iiiab irons pallasites seem to have formed by the intrusion of a highly evolved metallic magma from a iiiab like core into fragmented olivine of the overlying dunite mantle high cr contents are commonly encountered during the analyses of metallic samples of high au iiiab irons and main group pallasites an indication that cr contents were high in the intruding liquid and that cr behaved as an incompatible element during the crystallization of the iiiab magma contrary to expectations based on the negative iiiab cr ni and cr au trends among low au iiiab irons in a region about 10 cm across in the brenham main group pallasite massive chromite fills the interstices between olivine grains the site normally occupied by metal in brenham and other pallasites the massive chromite may have formed as a late cumulus phase because fe ni was also crystallizing its absence in the chromite rich region suggests a separation associated with differences in liquid buoyancy the coexisting chromite and olivine are zoned in the olivine feo is highest in pallasitic olivine metal regions lowest in rims adjacent to chromite and intermediate in the cores of these olivines chromite shows the opposite zoning with the highest feo contents at grain edges adjacent to olivine the observed gradients are those expected to form by fe mg exchange between olivine and chromite during slow cooling at subsolidus temperatures compared to normal brenham contents of phosphoran olivine and phosphates are higher in the chromitic pallasitic region we also report data for large to massive chromites present in pmg molong and in high au iiiab bear creek that like brenham formed from a highly evolved magma the bear creek chromite has a much lower mg content than that in the pallasites implying that in the pmg the mg was extracted from the olivine during high temperature reaction with the precipitating chromite there are other circumstantial arguments indicating that cr was incompatible in the metal during the crystallization of the iiiab magma with the concentration in the residual magma rising from an initial value of about 300 g g to a value around 700 g g when bear creek and brenham were formed we consider possible explanations for these negative cr au and cr ni trends and find the most probable one to be that they reflect sampling artefacts resulting from analysts avoiding visible chromite and the commonly associated phase fes when choosing metal samples

olivine grain growth in partially molten fe ni s a proxy for the genesis of pallasite meteorites abstract the origin of pallasites has been the focus of a number of recent studies yet their formation process remains elusive while the mechanism leading to the genesis of the sub group termed mixed type pallasites containing polygonal rounded and fragmental olivines simultaneously is unclear here we test the hypothesis of mixing of olivine fragments with fe ni s after a non destructive impact followed by annealing employing both experimental analogues and numerical models the experimental series evidenced that the addition of sulfur to olivine fe ni accelerates olivine grain growth though the growth rate is reduced when fe ni s is not fully molten this is shown to be the consequence of competing growth of olivine and fe ni grains numerical models satisfying available formation constraints from natural samples indicate that planetesimals with radii 200 km are favorable for the genesis of rounded olivine bearing pallasites by annealing of fragments in partially molten fe ni s moreover early mixing in the planetesimal can form regions containing olivine grains with different grain sizes that could explain the formation of mixed type pallasites

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

asteroids and meteorites origin of stony iron meteorites at mantle core boundaries abstract stony iron meteorites formed at the core mantle interfaces of small asteroidal parents the mesosiderites formed when the thick crust of a largely molten parent body 100 200 km in diameter foundered and sank through the mantle to the core pallasites formed in smaller parent bodies 50 100 km in which olivine crystals from the partially molten mantle sank to the core mantle interface and rafted there subsequent collisions stripped away the rocky mantles of both kinds of parent bodies exposing the stony iron surfaces of their cores to direct impacts which continue to knock off meteorite fragments

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

historical rates of salt marsh accretion on the outer bay of fundy we examine rates of salt marsh accumulation in three marshes of the outer bay of fundy at each marsh we selected a site in the high marsh with similar vegetation and thus similar elevation accretion rates were estimated by 137 cs 210 pb and pollen stratigraphy to estimate rates of change over periods of 30 100 and 170 years respectively these rates are compared with records from the two closest tide gauges saint john new brunswick and eastport maine to assess the balance of recent marsh accretion and sea level change averaged marsh accretion rates have ranged from 1 3 0 4 to 4 4 1 6 mm year 1 over the last two centuries recent rates are similar to the rate of sea level change recorded at eastport maine suggesting that they are in step with recent sea level change but very sensi tive to short term variation in relative sea level based on the pollen stratigraphy in the marsh sediments the marsh ac cretion rate was higher during the late 18th to early 19th century higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting

morphological analysis of olivine grains annealed in an iron nickel matrix experimental constraints on the origin of pallasites and on the thermal history of their parent bodies two types of pallasites can be distinguished on the basis of the grain shape of olivine rounded or angular it has been suggested that these two types of textures resulted from different degrees of annealing at high temperature in the parent body in order to characterize the kinetics of rounding of olivine grains in an fe ni matrix we carried out a series of annealing experiments using a mixture of olivine and fe ni powder we were able to reproduce at a miniature scale the range of textures in pallasites the rate of rounding was rapid enough to be observed and measured at the scale of a few micrometers to 20 m even though the experiments were performed below the solidus of the fe ni metal for instance grains 14 m in diameter became nearly spherical within 7 days at 1400 oc for the morphological analysis of olivine grains we used two independent techniques the critical diameter method and the gaussian diffusion resample method a new technique specially developed for our study both techniques indicate that the rounding time scale is proportional to the cube of the grain size and that morphological adjustments in our experiments occurred by volume diffusion in the olivine lattice not by surface diffusion along the olivine metal boundaries we used our experimental data to estimate the time scales required for the development of olivine metal textures in natural pallasites we determined that small scale rounding of olivine grains in a solid metal matrix can be produced within relatively short time intervals 100 years to produce rounded olivine grains 0 1 mm in radius at 1300 1400oc

main group pallasites thermal history relationship to iiiab irons and origin we have determined metallographic cooling rates below 975 k for eight main group mg pallasites from ni profiles across taenite lamellae of known crystallographic orientation in metallic regions with widmanstatten patterns comparison with profiles generated by modeling kamacite growth gave cooling rates ranging from 2 5 to 18 k myr relative cooling rates were also inferred from the sizes of cloudy zone particles in 28 mg pallasites 86 170 nm and tetrataenite bandwidths in 20 mg pallasites 1050 2170 nm as these parameters are positively correlated with each other and negatively correlated with the metallographic cooling rates these three different techniques show that mg pallasites cooled below 975 k at significantly diverse rates since samples from the core mantle boundary should have indistinguishable cooling rates mg pallasites could not have cooled at this location group iiiab irons which were previously thought to be core samples from the mg pallasite body have faster cooling rates 50 350 k myr and smaller cloudy zone particle sizes and tetrataenite bandwidths this shows that iiiab irons cooled faster than mg pallasites and could not plausibly be from the same body the absence of related iron meteorites and achondrites and our thermal constraints suggest that mg pallasites cooled at diverse depths in a pallasitic body consisting of well mixed olivine and metallic fe ni such a body may have formed during an impact on a differentiated asteroid or protoplanet that mixed olivine mantle fragments with residual ir poor molten metal from the out ermost part of a core that chemically resembled the iiiab core and was 80 fractionally crystallized separation of the solid core and most of the associated mantle may have resulted from a grazing hit and run impact with a larger protoplanet or asteroid thermal calculations suggest that the radius of the pallasitic body was 400 km but the likely presence of a regolith would reduce this estimate considerably 2010 elsevier ltd all rights reserved

sediment accretion and organic carbon burial relative to sea level rise and storm events in two mangrove forests in everglades national park abstract the goal of this investigation was to examine how sediment accretion and organic carbon oc burial rates in mangrove forests respond to climate change specifically will the accretion rates keep pace with sea level rise and what is the source and fate of oc in the system mass accumulation accretion and oc burial rates were determined via 210pb dating i e 100 year time scale on sediment cores collected from two mangrove forest sites within everglades national park florida usa enhanced mass accumulation accretion and oc burial rates were found in an upper layer that corresponded to a well documented storm surge deposit accretion rates were 5 9 and 6 5 mm yr 1 within the storm deposit compared to overall rates of 2 5 and 3 6 mm yr 1 these rates were found to be matching or exceeding average sea level rise reported for key west florida organic carbon burial rates were 260 and 393 g m 2 yr 1 within the storm deposit compared to 151 and 168 g m 2 yr 1 overall burial rates the overall rates are similar to global estimates for oc burial in marine wetlands with tropical storms being a frequent occurrence in this region the resulting storm surge deposits are an important mechanism for maintaining both overall accretion and oc burial rates enhanced oc burial rates within the storm deposit could be due to an increase in productivity created from higher concentrations of phosphorus within storm delivered sediments and or from the deposition of allochthonous oc climate change amplified storms and sea level rise could damage mangrove forests exposing previously buried oc to oxidation and contribute to increasing atmospheric co2 concentrations however the processes described here provide a mechanism whereby oxidation of oc would be limited and the overall oc reservoir maintained within the mangrove forest sediments

chemical zoning of olivine in several pallasites chemical zoning profiles of olivines in the esquel imilac and yamato 8451 pallasites were measured by using an electron probe microanalyzer in order to study their cooling histories pallasite olivines are considered to be compositionally uniform but show faint zoning for fe mg cao al2o3 cr2o3 and mno within a few hundred micrometers from the rim the cao al2o3 and cr2o3 contents of olivines in pallasites decrease gradually toward the rim the fe mg zoning and the mno enrichment in olivine rims of pallasite olivines may reflect a redox process on the basis of diffusion calculations to estimate the cooling rate by using chemical zoning of pallasite olivine the formation process of chemical zoning was discussed similar cooling rates obtained for the fe mg cao and mno profiles of an olivine imply that these zoning patterns formed during the same event

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

two stage formation of pallasites and the evolution of their parent bodies revealed by deformation experiments abstract pallasites stony iron meteorites predominantly composed of olivine crystals and fe ni metal are samples of the interior of early solar system bodies and can thus provide valuable insights into the formation of terrestrial planets however pallasite origin is controversial either sampling the core mantle boundary or the shallower mantle of planetesimals that suffered an impact we present high strain rate deformation experiments with the model system olivine fes melt gold melt to investigate pallasite formation and the evolution of their parent bodies and compare the resulting microstructures to two samples of seymchan pallasite our experiments reproduced the major textural features of pallasites including the different olivine shapes olivine aggregates and the distribution of the metal and sulfide phases these results indicate that pallasites preserve evidence for a two stage formation process including inefficient core mantle differentiation and an impact causing disruption metal melt injection and fast cooling within months to years olivine aggregates important constituents of angular pallasites are reinterpreted as samples of a partially differentiated mantle containing primordial metallic melt not stemming from the impactor the long term retention of more than 10 vol of metal melt in a silicate mantle sampled by olivine aggregates indicates high effective percolation thresholds and inefficient metal silicate differentiation in planetesimals not experiencing a magma ocean stage

solidus and liquidus temperatures and mineralogies for anhydrous garnet lherzolite to 15 gpa abstract a review of experimental data for systems pertaining to anhydrous fertile garnet lherzolite shows strong convergence in the liquidus and solidus temperatures for the range 6 5 15 gpa these can converge either to a common temperature or to temperatures which differ by only 100 c the major element composition of magmas generated by even minor degrees of partial melting may be similar to the primordial bulk silicate earth composition in an upper mantle stratigraphic column extending over 160 km in depth the convergence of the solidus and liquidus temperatures is a consequence of the highly variable d t d p of the fusion curves for minerals which crystallize in peridotite systems in particular d t d p for the forsterite fusion curve is much less than that for diopside and garnet whether or not the solidus and liquidus intersect the liquidus mineralogy for undepleted garnet lherzolite compositions changes from olivine at low pressures to pyroxene garnet or a complex pyroxene garnet solid solution at pressures in excess of 10 15 gpa geochemical data for the earliest archean komatiites are consistent with an upper mantle phase diagram having garnet as a liquidus phase for garnet lherzolite compositions at high pressures all estimates of the anhydrous solidus and liquidus for the range 10 15 gpa are consistent with silicate liquid compressibility data which indicate that olivine may be neutrally buoyant in ultramafic magmas at these pressures

fast grain growth of olivine in liquid fe s and the formation of pallasites with rounded olivine grains abstract despite their relatively simple mineralogical composition olivine fe ni metal fes pyroxene the origin of pallasite meteorites remains debated it has been suggested that catastrophic mixing of olivine fragments with fe ni s followed by various degrees of annealing could explain pallasites bearing solely or prevalently fragmented or rounded olivines in order to verify this hypothesis and to quantify the grain growth rate of olivine in a liquid metal matrix we performed a series of annealing experiments on natural olivine plus synthetic fe s mixtures the best explanation for the observed olivine grain size distributions gsd of the experiments are dominant ostwald ripening for small grains followed by random grain boundary migration for larger grains our results indicate that olivine grain growth in molten fe s is significantly faster than in solid sulphur free metal we used the experimentally determined grain growth law to model the coarsening of olivine surrounded by fe s melt in a 100 600 km radius planetesimal in this model an impact is responsible for the mixing of olivine and fe ni s numerical models suggest that annealing at depths of up to 50 km allow for i average grain sizes consistent with the observed rounded olivine in pallasites ii a remnant magnetisation of fe ni olivine inclusions as measured in natural pallasites and iii for the metallographic cooling rates derived from fe ni in pallasites this conclusion is valid even if the impact occurs several millions of years after the differentiation of the target body was completed

sea level rise sedimentary record and organic carbon fluxes in a low lying tropical coastal ecosystem abstract sea level rise one of the most evident effects of recent climate change is already impacting coastal ecosystems because of its low relief population increase and economic development during the last century the celestun lagoon is highly vulnerable to global change including sea level rise here we study a sediment core from a tropical saltmarsh to evaluate the impact of sea level rise on sediment accretion and carbon fluxes some geochemical indicators in a 210pb dated sediment core showed clear signals of marine influence this was reflected on increased accretion rates from 0 3 0 1 mm yr 1 in 1941 to 2 9 1 2 mm yr 1 in 2012 these accretion rates were similar to eustatic sea level rise and mean acceleration ranged from 0 037 0 22 mm yr 2 implying a slr by 2100 ranging from 14 to 86 cm the one century 1917 2013 organic carbon stock in sediments was calculated to be 10 1 0 2 mg c ha 1 during the same period the organic carbon flux corrected for organic carbon degradation increased from 7 3 g c m 2 yr 1 to 73 26 g c m 2 yr 1 attributed to the impact of sea level rise in this ecosystem this work shows that tropical saltmarshes may provide useful information on sea level rise and the presented methodology may be used where instrumental records do not exist or they are too short

la icp ms mapping of olivine from the brahin and brenham meteorites complex elemental distributions in the pallasite olivine precursor abstract to investigate the early history of olivine from the main group pallasites brahin and brenham we have spatially mapped their trace element distributions using laser ablation inductively coupled plasma mass spectrometry la icp ms brahin olivine interiors contain 100 200 m patches enriched in cr al ti v sc and ga separated by linear enrichments of p these structures bear no relation to current crystal morphologies rather cross cutting relationships suggest they predate olivine metal mixing brenham olivine also has internal variations for these elements by contrast ni and co concentrations in olivine from both meteorites decrease near crystal margins as expected for freezing in of profiles formed during diffusive re equilibration with metal during cooling brenham olivine also has decreasing al cr and ti near the margin correlations between concentrations of cr and al exist for individual brahin olivine grains but do not hold over multiple grains indicating a heterogeneous precursor al and ti are correlated over multiple grains in brahin interpreted as ti cations decorating pre existing al defects in brenham olivine similar geochemical trends exist but the cr al relationship probably represents both grain margin effects and pre existing internal heterogeneity the preservation of structure for elements which are normally fast diffusers in olivine hinges on coupled substitutions involving al which along with p diffuses much more slowly than most other elements under some conditions al concentrations in olivine are low and variable 3 33 ppm which is inconsistent with crystallisation from a normal silicate melt al in olivine thermometers indicate that pallasite olivine was formed in a low temperature environment following its delivery to the magma ocean core mantle boundary al p systematics were not substantially modified assuming diffusivities for al and p that are similar to si since they reside in the same crystallographic site and temperatures of 1600 1650 k from the melting point of the metal and the absence of orthopyroxene in pallasites an upper limit on the residence time of pallasite olivine of 1 ma can be inferred by the persistence of trace element detail over scales of 100 m following the olivine metal mixing event homogeneous ni and co distributions were modified by diffusion cr and v were partially modified al and p were essentially unchanged

paucity of sulfide in a large slab of esquel new perspectives on pallasite formation the 0 7 ton esquel meteorite found in patagonia before 1951 is a typical main group pallasite in most respects we examined petrographically a slab 1 m long having an area of 3000 cm2 that shows the typical pallasitic texture with fragmental olivine phase abundances in vol are olivine 66 metal 32 schreibersite 0 76 troilite 0 46 and chromite 0 31 esquel can be divided into four lithologies 1 pallasitic matrix consisting of olivine fragments embedded in metal 81 2 large 5 cm olivine nodules having low metal contents 18 3 massive metal 0 3 and 4 zones dominated by fes and fine olivine 0 7 main group pallasites appear to have formed by the intrusion of a highly evolved low ir high ni au and s metallic magma into fragmented olivine this model implies that fes should be abundant in main group pallasites and we had speculated that examination of an exceptionally large slab might reveal a high troilite content we found instead an exceptionally low fes content new compositional data confirm that esquel has a lower au content than other main group pallasites having similar ir contents literature data based however on relatively small sections suggest that high au pallasites have higher s contents than esquel but have lower s contents than expected from a trapped melt model we conclude that a relatively complex model is required to explain the origin of main group pallasites after intrusion the degree of crystallization of the metallic magma varied from location to location but in almost all cases an fes rich liquid either escaped or formed fes rich pallasitic rocks that are underrepresented in the meteorite inventory

rounded mineral inclusions in upper mantle peridotite abstract mantle derived peridotite xenoliths contain abundant olivine with rounded spinel and orthopyroxene inclusions and orthopyroxene with rounded olivine and spinel inclusions the shape change of spinel olivine and orthopyroxene inclusions from the primarily polyhedral outline to the spherical outline is governed by interfacial diffusion of oxygen in spinel the most sluggish atom due to reduction of total interfacial energy of the host inclusion system the critical radius of maximum rounded inclusions of spinel in olivine is a function of temperature and annealing time assuming that the activation energy for the interfacial diffusion is 40 70 kcal mol 1 and that the annealing time for the spinel lherzolite from salt lake crater in hawaii is 100 ma the annealing times for perioditites under the island arcs of japan are estimated to be 1 10 ma

formation of olivine textures in pallasites and thermal history of pallasites in their parent body an analysis of the textures of pallasites has been made using data concerning the kinetic and rheological properties of silicates and metals pallasites containing rounded olivines e g the springwater and brehnam pallasites have been heated to above the solidus temperature of the metallic iron phases 1270 k the rounded olivines of grain size 0 5 1 0 cm observed in the springwater pallasites were formed between 1270 and 1370 k on the other hand those of grain size 0 5 1 0 mm as found in the brehnam pallasites may have been heated to above 1370 k however the duration of heating at such high temperatures must have been less than 5 103 y pallasites containing angular olivines with microscopically rounded corners e g the eagle station dora pallasites have suffered shock events fracturing the olivine grains which may correspond to collisions during the accretional stage of the parent body and experienced successive annealing during cooling from a temperature between 1150 and 1270 k

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

magnesian anorthosites and a deep crustal rock from the farside crust of the moon abstract among over thirty lunar meteorites recovered from the hot deserts and antarctica dhofar 489 is the most depleted in thorium 0 05 ppm feo and rare earth elements ree dhofar 489 is a crystalline matrix anorthositic breccia and includes clasts of magnesian anorthosites and a spinel troctolite the mg mg fe mol mg numbers 75 85 of olivine and pyroxene grains in this meteorite are higher than those of the apollo ferroan anorthosites such materials were not recovered by the apollo and luna missions however remote sensing data suggest that the estimated concentrations of th and feo are consistent with the presence of such samples on the farside of the moon the differentiation trend deduced from the mineralogy of the anorthositic clasts define a magnesian extension of the ferroan anorthosite fan trend constructed from the apollo samples the presence of magnesian anorthositic clasts in dhofar 489 still offers a possibility that the farside trend with magnesian compositions is more primitive than the fan trend and may require a revision of this classical differentiation trend the ar ar age of dhofar 489 is 4 23 0 034 gyr which is older than most ar ages reported for highland rocks returned by apollo the old ar ar age of impact formation of this breccia and the presence of a fragment of spinel troctolite of deep crustal origin suggest that a basin forming event on the farside excavated the deep crust and magnesian anorthosites before formation of imbrium

grain growth in forsterite nickel mixtures analogues of small parent bodies during early accretion abstract we report an experimental study on the grain growth kinetics and microstructural evolution of olivine metal systems 32 experiments have been performed on four different mixtures of forsterite fo and nickel ni respectively in vol 95 5 80 20 30 70 and 10 90 all experiments were carried out at high temperature 1440 c at oxygen fugacity fo 2 3 log units below the ni nio buffer and for durations between 2 h and 21 days in aggregates containing isolated forsterite grains in a nickel matrix fo ni 10 90 forsterite did not grow and grain growth of nickel was abnormal in all other cases features of normal grain growth were observed and the data were fit to the classic grain growth law d n d 0 n kt for all these aggregates grain growth exponents are in the range 4 0 n nichols and mackwell 1991 for porous olivine aggregates both ni and pores apparently behaving as mobile minor phases extrapolation to time scales relevant to the formation of ordinary chondrite parent bodies shows that mean grain sizes reached fo and ni are of the same order of magnitude 100 m to 1 mm as those observed in several types of meteorites iron rich phases kamacite taenite and or troilite in several h chondrites are shown to present normal grain growth features and ngsd shapes similar to those in our experimental samples where nickel grains are not interconnected i e fo ni 95 5 and 80 20 the grain growth mechanism for the iron rich phases in these meteorites may thus also occur by coalescence rate limited by grain boundary migration of olivine

accretion rates in coastal wetlands of the southeastern gulf of california and their relationship with sea level rise sea level rise slr is one of the most conspicuous examples of the environmental impact of recent climate change since slr rates are not uniform around the planet local and regional data are needed for proper adaptation plans 210pb dated sediment cores were analyzed to determine the trends of sediment accretion rates sars at three tropical saltmarshes in the estero de urias lagoon gulf of california mexico in order to estimate the slr trends during the past 100 years under the assumption that these ecosystems accrete at a similar rate to slr a chemometric approach including multivariate statistical analysis factor analysis of geochemical data including 13c 15n c n ratios and br na and cl as proxies for marine transgression was used to identify the marine transgression in the sediment records based on core geochemistry only one of the three cores provided a long term record attributable to marine transgression slr trends estimated from sars showed increasing values from a min

intrinsic oxygen fugacity measurements on seven chondrites a pallasite and a tektite and the redox state of meteorite parent bodies abstract intrinsic oxygen fugacity fo2 measurements were made on five ordinary chondrites a carbonaceous chondrite an enstatite chondrite a pallasite and a tektite results are of the form of linear log f o 2 1 t plots except for the enstatite chondrite measured results agree well with calculated estimates by others the tektite produced fo2 values well below the range measured for terrestrial and lunar rocks the lowpressure atmospheric regime that is reported to follow large terrestrial explosions coupled with a very high temperature could produce glass with fo2 in the range measured the meteorite salta pallasite has low fo2 and lies close to hvittis e6 unlike the other samples results for salta do not parallel the iron wustite buffer but are close to the fayalite quartz iron buffer in slope minor reduction by graphite appears to have taken place during metamorphism of ordinary chondrites fo2 values of unequilibrated chondrites show large scatter during early heating suggesting that the constituent phases were exposed to a range of fo2 conditions the samples equilibrated with respect to fo2 in relatively short time on heating equilibration with respect to fo2 in ordinary chondrites takes place between grades 3 and 4 of metamorphism application of p t fo2 relations in the system c co co2 indicates that the ordinary chondrites were metamorphosed at pressures of 3 20 bars as it appears that they lay on the graphite surface a steep positive thermal gradient in a meteorite parent body lying at the graphite surface will produce thin reduced exterior an oxidized near surface layer and an interior that is increasingly reduced with depth a shallow thermal gradient will produce the reverse a body heated by accretion on the outside will have a reduced exterior and oxidized interior meteorites from the same parent body clearly are not required to have similar redox states