iron magnesium order disorder in an orthopyroxene crystal from the johnstown meteorite abstract equilibrium reversals of fe 2 mg distribution between the m1 and m2 sites of an orthopyroxene from the johnstown meteorite were achieved at several temperatures between 700 and 1000 c one single crystal was used for the whole thermal treatment and for collecting all the x ray data after quenching the intracrystalline ion exchange for the bulk chemical composition mg 1 453 fe 0 441 cr 0 024 ca 0 054 mn 0 015 fe 0 005 ti 0 003 al 0 005 si 1 960 al 0 040 o 6 is given by ln k d 3027 39 t k 0 872 0 013 where k d is the distribution coefficient for the reaction fe m2 2 mg m1 mg m2 fe m1 2 a transmission electron microscopy tem study of part of the crystal showed the presence of very thin augite lamellae and guinier preston zones indicating a relatively rapid cooling of the host rock at temperatures close to 1000 c the new temperature scale yields a relatively high quenching temperature of 379 8 c for the pyroxene which appears consistent with a rapid cooling estimated few degrees per hundred years of a magmatic cumulate excavated by an impact on its parental body

cooling history of some antarctic ureilites to obtain some constraints on the cooling histories of ureilites we have studied the chemical zoning of olivines and the compositional variations of pyroxenes in the pca82506 y790981 and alh77257 ureilites using an electron microprobe fayalite components and cao contents in olivines show a gradual decrease toward the rims the mno feo variation of ureilite pyroxenes shows a subtle anticorrelation that is probably related to the redox reaction during their original crystallization the chemical variation within a grain of y790981 pigeonites may be attributed to partial melting due to shock heating cooling rates of 2 6 c hour have been obtained from diffusional calculations based on the reverse zoning profile of fa components at the grain boundary of ureilite olivines we assume that iron diffusion controls the reduction reaction although the reduction process may be more complex because iron diffusion is slower in pyroxene than in olivine ureilite pigeonite would not show chemical zoning by reduction if their cooling rates were faster than about 1 c hour this result is consistent with impact produced excavation of the ureilite parent mass

spectral reflectance properties of ureilites abstract the 0 35 2 6 m reflectance spectra of 18 ureilites have been examined in order to improve our understanding of the spectral reflectance properties of this meteorite class across this spectral range ureilite spectra are characterized by a steep rise in reflectance over the 0 3 to approximately 0 7 m range low overall reflectance 25 and weak mafic iron silicate absorption bands in the 1 and 2 m region the weakness of these bands and the low reflectance are attributed to the presence of dispersed graphite and related carbonaceous phases metal and possibly shock wavelength positions of the mafic silicate absorption bands span a range of values but are consistent with the presence of pyroxene and olivine ureilite spectra generally exhibit blue slopes across the 0 7 2 6 m interval and exhibit many overall similarities to some carbonaceous chondrites the weak features and spectral diversity of ureilites make reflectance spectroscopy based identification of a ureilite parent body challenging as terrestrial alteration of ureilites is prevalent spectral studies of falls are most useful for determining the spectral properties of likely parent bodies

magmatic inclusions and felsic clasts in the dar al gani 319 polymict ureilite magmatic inclusions occur in type ii ureilite clasts olivine orthopyroxene augite assemblages with essentially no carbon and in a large isolated plagioclase clast in the dar al gani dag 319 polymict ureilite type i ureilite clasts olivine pigeonite assemblages with carbon as well as other lithic and mineral clasts in this meteorite are described in ikeda et al 2000 the magmatic inclusions in the type ii ureilite clasts consist mainly of magnesian augite and glass they metastably crystallized euhedral pyroxenes resulting in feldspar component enriched glass on the other hand the magmatic inclusions in the large plagioclase clast consist mainly of pyroxene and plagioclase with a mesostasis they crystallized with a composition along the cotectic line between the pyroxene and plagioclase liquidus fields dag 319 also contains felsic lithic clasts that represent various types of igneous lithologies these are the rare components not found in the common monomict ureilites porphyritic felsic clasts the main type contain phenocrysts of plagioclase and pyroxene and their groundmass consists mainly of plagioclase pyroxene and minor phosphate ilmenite chromite and or glass crystallization of these porphyritic clasts took place along the cotectic line between the pyroxene and plagioclase fields pilotaxitic felsic clasts crystallized plagioclase laths and minor interstitial pyroxene under metastable conditions and the mesostasis is extremely enriched in plagioclase component in spite of the ubiquitous crystallization of plagioclase laths in the clasts we suggest that there are two crystallization trends pyroxene metal and pyroxene plagioclase trends for the magmatic inclusions and felsic lithic clasts in dag 319 the pyroxene metal crystallization trend corresponds to the magmatic inclusions in the type ii ureilite clasts and the pilotaxitic felsic clasts where crystallization took place under reducing and metastable conditions suppressing precipitation of plagioclase the pyroxene plagioclase crystallization trend corresponds to the magmatic inclusions in the isolated plagioclase clast and the porphyritic felsic clasts this trend developed under oxidizing conditions in magma chambers within the ureilite parent body the felsic clasts may have formed mainly from albite component rich silicate melts produced by fractional partial melting of chondritic precursors the common monomict ureilites type i ureilites may have formed by the fractional partial melting of alkali bearing chondritic precursors however type ii ureilites may have formed as cumulates from a basaltic melt

antarctic fro90011 lodranite cooling history from pyroxene crystal chemistry and microstructure the antarctic fro90011 lodranite shows an achondritic coarse granoblastic texture with an approximately chondritic composition the crystal chemistry of pbca and c2 c pyroxene single crystals and the tem texture of pbca pyroxene were investigated to reconstruct the evolutionary history of the meteorite parent body the structural behaviour of orthopyroxene en85fs12 4wo2 6 is well constrained in the en fs trend orthopyroxene fe2 mg ordering in the m1 and m2 sites yields a closure temperature tc of 570 20 c and a cooling rate 10 c day near the tc clinopyroxene is a low iron augite en51fs5wo44 clinopyroxene fe2 mg ordering in the m1 and m2 sites yields a tc of 513 50 c which is compatible with the cooling rate derived from the orthopyroxene crystals tem investigation on orthopyroxene showed a few thin lamellae not larger than 20a parallel to 100 and rare one unit cell guinier preston zones tem eds analysis did not reveal significant chemical differences between lamella rich and lamella free zones the above data are interpreted as being due to fast cooling resulting from radiative heat loss of small fragments ejected from a parent body which were subsequently reassembled into a larger body

extremely high energy wave deposits inside the great barrier reef australia determining the cause tsunami or tropical cyclone abstract a hydrodynamic approach is used to determine whether tsunami or cyclone generated waves were responsible for the deposition of fields of well imbricated rock boulders up to 290 tonnes along the coast of cairns inside the great barrier reef australia calculations of the overturning moments show that only tsunami are capable of moving such large boulders in this environment it is hypothesised that large tsunami 11 m have been able to penetrate the great barrier reef through wide 5 10 km 50 70 m deep passages between individual reefs three such passages each approximately 35 km apart and oriented in the same direction exist in the cairns region it is possible that these passages have funnelled and amplified palaeotsunamis the preferential location of eroded coral boulders up to 3 m in length on reef flats alongside these passages and their absence on other reefs throughout the region provide further evidence that extremely high energy waves have been able to penetrate the great barrier reef into the inner channel adjacent to the mainland carbon 14 ages of the coral boulders on these reef flats matches closely the ages of coral fragments pinned below the very large rock boulders along the coast these ages suggest that the cairns region has experienced large tsunami twice over the last millennium

numerical models of tsunami sediment transport current understanding and future directions abstract researchers who study tsunami deposits share common ultimate goals of their work which are to better assess the magnitude information of paleotsunamis and to contribute to the assessment of future tsunami risks numerical modeling of tsunami sediment transport is an important piece of interdisciplinary research that fills the gap between geological studies and practical utilization of tsunami deposits forward and inverse numerical models that address tsunami transport of sand and boulders have been developed over the last two decades forward models are capable of delineating the time evolution of tsunami hydrodynamics sediment transport and the resulting morphological changes associated with erosion and deposition inverse models estimate tsunami characteristics such as flow speed and depth from deposits numerical modeling can be used not only to quantify paleotsunamis but also to enhance our understanding of tsunami sedimentology and hydrodynamics to make progress towards the ultimate goal of improved tsunami risk assessment development of an in depth mutual understanding between modelers and geologists of the advantages limitations and uncertainties in both numerical modeling and geological records is an important challenge

mineralogy of coexisting pyroxenes in magnesian ureilites and their formation conditions abstract the occurrence of orthopyroxene in two magnesian ureilites found in antarctica yamato y 791538 and lew85440 has been confirmed by electron probe microanalysis and by single crystal x ray diffraction the first coexisting equilibrium pigeonite orthopyroxene pair has been found in y791538 the lew85440 orthopyroxene coexists with minor augite the orthopyroxenes and olivines in y791538 y74659 and lew85440 have almost identical compositions but the ca contents of their coexisting clinopyroxenes differ considerably these phase assemblages can be explained by crystallization of mafic silicates with a similar composition oxygen fugacity and oxygen isotope anomaly at different temperature above 1220 c the high temperature crystallization of refractory mg rich silicates and the possible preservation of the oxygen isotope anomaly of precursor carbonaceous chondrites like materials may be consistent with their formation processes probably through local melting of more matrices than mg rich silicates and crystal growth induced by the planetesimal scale collision

transmission electron microscope texture and crystal chemistry of coexisting ortho and clinopyroxene in the antarctic ureilite frontier mountain 90054 implications for thermal history frontier mountain fro 90054 from antarctica is a rare clino and orthopyroxene bearing ureilite with a coarse equigranular oriented texture grains up to 3 mm it is classified as a low shock ca rich type the crystal chemistry of its clinopyroxene wo39 3en54 6fs6 1 orthopyroxene en84 2fs11wo4 8 and olivine fa12 6fo86 9 was investigated by single crystal x ray structural refinements and transmission electron microscope tem observations to obtain data on the evolutionary history of the parent body the m1 octahedron and unit cell volumes of the orthopyroxene and clinopyroxene are consistent with low pressure crystallization the closure temperatures for intracrystalline mg fe2 ordering yielded values of 674 c and 804 c for opx and 596 c for cpx which indicate high temperature equilibration and fast cooling trasmission electron microscope investigations were performed on clinopyroxene orthopyroxene and pigeonite the 100 twin lamellae in the clinopyroxene and intergrowth of clino and orthoenstatite lamellae in orthopyroxene most probably originated by deformation exsolution was not observed in any of the phases which suggests rapid cooling analysis by tem also revealed interstitial na rich glass and pigeonite with sharp h k odd reflections and rare stacking faults parallel to 100 textural and crystal chemical data obtained by tem indicated rapid cooling that was probably due to fast radiative heat loss as a result of the disintegration of the parent body into small fragments which subsequently reassembled into a larger body one or more collisional events caused fine scale stacking faults and partial melting

northwest africa 1500 plagioclase bearing monomict ureilite or ungrouped achondrite northwest africa nwa 1500 is an ultramafic meteorite dominated by coarse 100 500 m olivine 95 96 augite 2 3 and chromite 0 6 1 6 in an equilibrated texture plagioclase 0 7 1 8 occurs as poikilitic grains up to 3 mm in vein like areas that have concentrations of augite and minor orthopyroxene other phases are cl apatite metal sulfide and graphite olivine ranges from fo 65 73 with a strong peak at fo 68 69 most grains are reverse zoned and also have 10 30 m reduction rims in terms of its dominant mineralogy and texture nwa 1500 resembles the majority of monomict ureilites however it is more ferroan than known ureilites fo 75 and other mineral compositional parameters are out of the ureilite range as well furthermore neither apatite nor plagioclase have ever been observed and chromite is rare in monomict ureilites nevertheless this meteorite may be petrologically related to the rare augite bearing ureilites and represent a previously unsampled part of the ureilite parent body upb the mn mg ratio of its olivine and textural features of its pyroxenes are consistent with this interpretation however its petrogenesis differs from that of known augite bearing ureilites in that 1 it formed under more oxidized conditions 2 plagioclase appeared before orthopyroxene in its crystallization sequence and 3 it equilibrated to significantly lower temperatures 800 1000 c from two pyroxene and olivine chromite thermometry formation under more oxidized conditions and the appearance of plagioclase before orthopyroxene could be explained if it formed at a greater depth on the upb than previously sampled however its significantly different thermal history compared to ureilites may more plausibly be explained if it formed on a different parent body this conclusion is consistent with its oxygen isotopic composition which suggests that it is an ungrouped achondrite nevertheless the parent body of nwa 1500 may have been compositionally and petrologically similar to the upb and may have had a similar differentiation history

are ureilites residues from partial melting of chondritic material the answer from magpox calculations performed using magpox show that no bulk compositions having chondritic ca al ratio and within the range of chondritic si mg ratios can produce the olivine pigeonite ureilites which constitute 65 of those for which modal abundances are known as residues of single stage equilibrium partial melting calcium aluminum ratios of 2 3 5 ci are required in addition all the ureilites could not have formed from a single composition at various degrees of reduction because they show no correlation between pigeonite olivine ratio and mg ratio materials with various al mg ratios ranging from subchondritic to superchondritic are required if these materials are primitive i e created by nebular processes rather than planetary igneous processes they are unknown in the meteorite record excess accretion relative to chondrites of 5 10 mol of a high temperature condensate component which was itself almost completely depleted in corundum due to early fractionation could create the necessary compositions the plausibility that such processes occurred on a parent body sized scale is difficult to assess in contrast lodranites can be produced as residues of 3 30 equilibrium partial melting of an average ordinary chondritic composition at the appropriate level of reduction although many features of ureilites suggest that they are relatively primitive residues produced by low degrees of melting of chondritic materials and thus resemble lodranites and other groups of primitive achondrites their predominantly pigeonite olivine mineralogy remains difficult to explain within this simple scenario

tem investigations on the monomict ureilites jalanash and hammadah al hamra 064 we studied the petrography and mineralogy of two monomict ureilites hammadah al hamra 064 hh064 and jalanash by using reflected light and scanning electron microscopy quantitative analyses were performed by electron microprobe and the microstructures were investigated with transmission electron microscopy tem hh064 features two different textures a poikilitic and a typical one whereas jalanash shows only the typical ureilite texture our synergetic chemical and microstructural investigations reveal a complex cooling history for both ureilites the temperature for the first equilibrium deduced from the pigeonite augite assemblage in hh064 is 1200 c the presence of antiphase domains in low ca pyroxenes proves that they are clearly pigeonite the occurrences of tweed microstructure and orthopyroxene lamellae which are incompletely developed imply a faster cooling rate from the first equilibrium with a sudden end although both ureilites contain shock induced diamonds dislocations in silicates are rare this observation suggests that the meteorites were hot at the time of strong shock metamorphism or that they were heated after strong shock metamorphism after this event new microstructural features were generated by different cooling processes and were frozen by a final rapid decrease in temperature possibly due to excavation from the ureilite parent body or bodies

wave emplaced coarse debris and megaclasts in ireland and scotland boulder transport in a high energy littoral environment abstract many coastlines of the world particularly those at higher latitudes and those located in tropical cyclone belts are regularly battered by strong storm waves drowning of low lying areas by storm surges and storm floods has been thoroughly recorded however storm deposits at rocky shorelines or on cliffs have been underrepresented in the literature this article presents observations of extraordinary wave deposits along the high wave energy coastlines of western ireland and the northern scottish isles and discusses possible wave event types and time windows of the processes responsible we used archaeological geomorphological and geochronological disciplines to compare our findings with earlier results published for these areas and to contribute to the debate on whether large clasts found well above sea level and or a considerable distance inland were deposited by storms or by tsunamis

thermal history of mesosiderites quantitative constraints from compositional zoning and fe mg ordering in orthopyroxenes abstract we have derived mathematical relations to calculate cooling rates from the extent of compositional zoning developed during cooling across the interface of a natural diffusion couple these relations were used to calculate the high temperature cooling rates of the mesosiderites lowicz and clover springs from the available data on compositional zoning across core overgrowth interface of orthopyroxene grains we have also determined the cation ordering in four selected orthopyroxene crystals from bondoc and estherville mesosiderites with very high precision and used these data to calculate their low temperature cooling rates the compositional zoning of orthopyroxene crystals reflects extremely rapid cooling rates at least 1 c 100 years in the temperature range 850 1150 c however simultaneous consideration of both metallographic and cation ordering data for estherville within the framework of either an asymptotic or an exponential cooling model requires a cooling rate of l c ma near 250 c the cation ordering data for bondoc for which no metallographic data are yet available are suggestive of even slower cooling rate which implies excavation from a somewhat greater depth in the parent body however within the limits of their uncertainties the measured site occupancies of the orthopyroxene crystals from bondoc can be reconciled with a cooling rate similar to that of estherville the calculated cooling rates at both high and low temperatures have been used to develop a thermal evolution model of mesosiderites the suggested model is not incompatible with an asteroidal parent body for these meteorites further it is shown that the closure temperature of ar ar age must be tied to the slow cooling rate below 500 c

waves coastal boulder deposits and the importance of the pre transport setting the pre transport environment of a coastal boulder along with its shape size and density determines the height of wave required for it to be transported different forces act on sub aerial boulders as opposed to submerged boulders when struck by a wave boulders derived from joint bounded blocks on shore platforms predominantly experience lift force and require a wave of greater height to be transported than boulders in other environments no one equation is applicable to determine the height of palaeo waves responsible for depositing a field or ridge of imbricated coastal boulders a range of equations and their derivation is presented here which can be applied to the respective pre transport environment of a boulder such an approach is necessary when attempting to reconstruct the frequency and magnitude of past coastal wave hazards and for differentiating between tsunami and storm wave deposited boulder fields

comment on reassessment of hydrodynamic equations minimum flow velocity to initiate boulder transport by high energy events storms tsunamis by n a k nandasena r paris and n tanaka marine geology 281 70 84 abstract studies of coastal boulder deposits have dramatically increased in number during the last decade these have been accompanied by modeling efforts to understand the initiation of transport and the transport itself a recent article by nandasena et al 2011 has attempted to improve equations developed by nott 1993 2007 for the movement initiation of boulders but we argue that these equations are not appropriate for the tsunami data at least in north sumatra used to reassess nott s set of equations indeed the field work on which the discussed article is partially based is inconsistent with the findings the sand beach context and the distribution of these boulder deposits may invalidate the modeling approach of the authors it is very unlikely that water alone was able to initiate the transport of the limestone clasts the role of the smaller fractions must be assessed as these were an important component of the 2004 boxing day tsunami waves moreover the spatial distribution of the boulder deposits which part of the discussed article relies on and that has been described in a previous paper is not consistent with the inferences drawn in the present article the deposit has been described as a mix of boulders of various sizes and weight concentrated in space without landward fining this suggests an en masse deposit rather than a deposit related to a progressive reduction of water velocity such en masse deposits have been related in different environments to debris flows hence we suggest that this modeling needs to take into account smaller sediments and eventually move towards a bingham flow concept for the case of tsunami waves

constraints on the cooling rates of chondrules from the microstructure of clinopyroxene and plagioclase abstract attempts are made to quantify cooling rates of chondrules from the microstructure of clinopyroxene and ca rich plagioclase pigeonite diopside exsolution lamellae on 001 are frequently observed in allende granular olivine pyroxene chondrules cooling rates of 2 10 c h are obtained for the observed wavelengths between 25 and 33 nm from isothermal time temperature transformation diagrams modelling of lamellae growth during cooling yields similar cooling rates between 7 and 25 c h coarsening of pigeonite diopside exsolution lamellae takes place in the small temperature interval from approximately 1350 to 1200 c the occurrence of type b antiphase domains in ca rich plagioclase provides independent constraints on chondrule cooling rates isothermal time temperature transformation diagrams yield cooling rates of approximately 3 30 c h for the observed domain sizes between 10 and 30 nm cooling rates derived from antiphase domains in plagioclase are valid in approximately the same temperature range than those deduced from pigeonite diopside exsolution lamellae our estimates must be regarded as upper limits and they seem to be significantly lower than those derived from dynamic crystallization experiments 100 2000 gc h as dynamic crystallization experiments yield cooling rates at higher temperatures near the liquidus this observation may suggest nonlinear cooling the absence of orthoenstatite lamellae in clinoenstatite indicates high cooling rates on the order of 10 4 c h at temperatures around 1000 c

small is beautiful the analysis of nanogram sized astromaterials the capability of modern methods to characterize ultra small samples is well established from analysis of interplanetary dust particles idps interstellar grains recovered from meteorites and other materials requiring ultra sensitive analytical capabilities powerful analytical techniques are available that require under favorable circumstances single particles of only a few nanograms for entire suites of fairly comprehensive characterizations a returned sample of 1000 particles with total mass of just 1 g permits comprehensive quantitative geochemical measurements that are impractical to carry out in situ by flight instruments the main goal of this paper is to describe the state of the art in microanalysis of astromaterials given that we can analyze fantastically small quantities of asteroids and comets etc we have to ask ourselves how representative are microscopic samples of bodies that measure a few to many kilometers across with the galileo flybys of gaspra and ida it is now recognized that even very small airless bodies have indeed developed a particulate regolith acquiring a sample of the bulk regolith a simple sampling strategy provides two critical pieces of information about the body regolith samples are excellent bulk samples because they normally contain all the key components of the local environment albeit in particulate form furthermore because this fine fraction dominates remote measurements regolith samples also provide information about surface alteration processes and are a key link to remote sensing of other bodies studies indicate that a statistically significant number of nanogram sized particles should be able to characterize the regolith of a primitive asteroid although the presence of larger components e g chondrules calcium aluminum rich inclusions large crystal fragments etc within even primitive meteorites e g murchison points out the limitations of using data obtained from nanogram sized samples to characterize entire primitive asteroids however the most important asteroidal geological processes have left their mark on the matrix because this is the finest grained portion and therefore most sensitive to chemical and physical changes thus the following information can be learned from this fine grain size fraction alone 1 mineral paragenesis 2 regolith processes 3 bulk composition 4 conditions of thermal and aqueous alteration if any 5 relationships to planets comets meteorites via isotopic analyses including o 6 abundance of water and hydrated material 7 abundance of organics 8 history of volatile mobility 9 presence and origin of presolar and or interstellar material most of this information can be obtained even from dust samples from bodies for which nanogram sized samples are not truly representative future advances in sensitivity and accuracy of laboratory analytical techniques can be expected to enhance the science value of nano to microgram sized samples even further this highlights a key advantage of sample returns that the most advanced analysis techniques can always be applied in the laboratory and that well preserved samples are available for future investigations

seamounts in a restless ocean response of passive tracers to sub tidal flow variability 1 the action of sub tidal oceanic flow impinging on an isolated seamount and its consequences for biological tracer patterns was assessed using a three dimensional ocean circulation model passive tracers released above an isolated gaussian seamount were exposed to variations of flow magnitude frequency direction and seamount height the evolving patterns indicate significant qualitative differences steady and amplitude modulated unidirectional inflows generate advective downstream particle loss and patchiness non uniform inflow reduces advective particle loss and tracers are systematically redistributed and aggregated around the seamount summit tracer retention is mainly controlled by flow magnitude and summit depth variations of flow period were of lesser importance two important biological implications arise from this study first particle dynamics at isolated seamounts is strongly constrained by mesoscale variability of the sub tidal far field flow secondly the influence of seamounts on particle distribution is not restricted to local and small scale phenomena but can penetrate deep into the oceanic far field on a scale of tens to hundreds of kilometers

microtextures and crystal chemistry of pigeonite in the ureilites alha77257 rkpa80239 y 791538 and alha81101 the microtextures of pigeonite in four ureilites allan hills alh 77257 reckling peak rkp a80239 yamato y 791538 and allan hills a81101 chosen to span a range of composition and shock level were investigated by transmission electron microscopy tem two of the samples were also investigated by single crystal x ray diffraction to determine fe2 mg cation site partitioning the low shock and compositionally homogeneous pigeonites in alha77257 and rkpa80329 wo 6 4 for both mg 86 3 and 84 3 respectively display irregularly spaced shock induced stacking faults oriented parallel to 100 and largeantiphase domains 50 100 nm antiphase domains have no preferential orientation no evidence of exsolution was observed the low shock y 791538 pigeonite is homogeneous and has higher ca and mg wo 9 4 mg 91 2 tem investigation showed spinodal decomposition indicative of incipient exsolution small antiphase domains were observed 5 nm single crystal refinement yielded r4 5 71 with fe2 mg partitioning coefficient kd 0 077 8 and tc 658 35 c alha81101 has compositionally heterogeneous pyroxenes with large local variations in wo and mg wo 4 13 mg 86 68 no compositional gradients from core to rim of grains were observed and the heterogeneity is interpreted as related to cation migration during shock in one relatively ca rich region wo 12 tem analysis showed augite pigeonite exsolution lamellae with spacing 145 20 nm results for alha77257 rkpa80239 and y 791538 support a model of rapid cooling following breakup of the ureilite parent body the presence of exsolution lamellae in alha81101 can be related to a local shock induced ca enrichment and provides no constraint on the late cooling history

the use of boulders for characterising past tsunamis lessons from the 2004 indian ocean and 2009 south pacific tsunamis tsunamis are high energy events capable of transporting extremely heavy loads including boulders we compare boulder deposits created by two modern tsunami events the 2004 indian ocean and the 2009 south pacific tsunamis where the boulder sources were in similar topographic settings and for which we have accurate data on the wave characteristics boulder distribution preferential orientation and numerical simulation of boulder transport are discussed a comparison between the impacts of the south pacific and indian ocean tsunamis shows similar characteristics such as limited landward extent and the absence of landward fining differences between the results from modelling and field data are most probably caused by variables such as coastal plain roughness buildings trees microtopography particle shape and boulder collision during transport that are summarised as coefficients in the mathematical models characterising modern events through coarse sediment deposits provides valuable information to help identify and interpret palaeo tsunami imprints on coastal landscapes

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

mineralogy of antarctic ureilites and a working hypothesis for their origin and evolution abstract mineralogical and crystallographic data and electron microprobe analyses of silicate minerals for antarctic ureilites y74123 y74130 y74659 y790981 alha77257 alha78019 and alh82106 extend the chemical and textural variations among ureilites beyond those known for non antarctic ureilites low ca pyroxenes possibly orthopyroxene poikilitically enclosed in olivine and coexisting with mg rich pigeonites have been identified in y74659 and alha77257 coexisting low ca pyroxene pigeonite and augite together with the very fe rich olivine in ureilites were observed in y74130 almost fe free pigeonite and diopside coexist in alh82106 no systematic differentiation trend has been reconstructed from these data but the pyroxene pairs yield formation temperatures above 1200 c a weak anticorrelation between mno and feo delineated by these pyroxenes suggests that a reduction reaction is responsible for the chemical variations a working hypothesis for ureilite formation involves high temperature episoded and a planetesimal scale collision which might have facilitated compaction and recrystallization of mafic silicates during the episodes fe ni s eutectic melt and a partial melt rich in ca al and fe might have been lost from a carbonaceous chondrite like source material

reassessment of hydrodynamic equations minimum flow velocity to initiate boulder transport by high energy events storms tsunamis abstract coastal boulders are good evidence of high energy events but the distinction between storm and tsunami boulders remains difficult to identify and mathematical models are still in their preliminary stages in a pioneering contribution nott 1997 2003 developed hydrodynamic equations to assess the minimum wave height required to initiate transport of a coastal boulder by tsunamis or storm surges these equations are widely cited and used but they can be improved in this study nott s equations have been revised 1 the equation for the submerged boulder scenario has been revised by rearranging the lift area of the lift force 2 the subaerial boulder scenario has been reconsidered by rearranging lift area and omitting inappropriate use of inertia force and 3 the joint bounded scenario was revised by balancing force components in the lifting direction and the effect of slope at the pre transport location is tested calculations are performed for four case studies boulders in western and eastern australia data after nott 1997 2003 boulders in southeastern italy data after scicchitano et al 2007 storm boulders in iceland data after etienne and paris 2010 and 2004 tsunami boulders in sumatra data after paris et al 2009 the minimum flow velocity required to initiate the transport of submerged boulders in the revised equation is less than that in nott s equation e g reductions up to 56 for submerged boulders and 65 for joint bounded blocks the minimum flow velocity required to initiate the transport of subaerial boulders from the revised equation also differed in comparison with nott s equation e g 4 22 for boulders detached from a seawall by the 2004 tsunami in sumatra while nott s equation was not applicable to some boulders e g beach rock boulders transported from the nearshore by the 2004 tsunami if we consider a joint bounded scenario for storm boulders in iceland the minimum flow velocity differs 43 to 41 from the results from nott s equation a boulder transport histogram is then introduced to represent the range of flow velocity that satisfies the requirements for initial transport of a boulder in different modes sliding rolling and saltation the boulder transport histogram can be used to predict the possible initial transport mode of a boulder from the flow velocity these theoretical results are compared to field data thus suggesting the initial transport mode of boulders and their pre transport locations the boulder transport histogram would be a valuable tool to reconstruct the magnitude of prehistoric high energy events such as tsunamis or storm surges in terms of flow velocity

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

tsunamis as geomorphic crises lessons from the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract large tsunamis are major geomorphic crises since they imply extensive erosion sediment transport and deposition in a few minutes and over hundreds of kilometres of coast nevertheless little is known about their geomorphologic imprints the december 26 2004 tsunami in sumatra indonesia was one of the largest and deadliest tsunamis in recorded human history we present a description of the coastal erosion and boulder deposition induced by the 2004 tsunami in the lhok nga bay located to the west of banda aceh northwest sumatra the geomorphological impact of the tsunami is evidenced by beach erosion some beaches have almost disappeared destruction of sand barriers protecting the lagoons or at river mouths numerous erosion escarpments typically in the order of 0 5 1 5 m when capped by soil and more than 2 m in dunes bank erosion in the river beds the retreat along the main river is in the order of 5 15 m with local retreats exceeding 30 m large scars typically 20 50 cm deep on slopes dislodgement of blocks along fractures and structural ramps on cliffs the upper limit of erosion appears as a continuous trimline at 20 30 m a s l locally reaching 50 m the erosional imprints of the tsunami extend to 500 m from the shoreline and exceed 2 km along riverbeds the overall coastal retreat from lampuuk to leupung was 60 m 550 000 m 2 and locally exceeded 150 m over 276 000 m 3 of coastal sediments were eroded by the tsunami along the 9 2 km of sandy coast the mean erosion rate of the beaches was 30 m 3 m of coast and locally exceeded 80 m 3 m the most eroded coasts were tangent to the tsunami wave train which was coming from the southwest the fringing reefs were not efficient in reducing the erosional impact of the tsunami the 220 boulders measured range from 0 3 to 7 2 m large typically 0 7 1 5 m with weights from over 50 kg up to 85 t we found one boulder less than 1 m large at 1 km from the coastline but all the others were transported less than 450 m 30 m and the moderate tsunamis height